public Guid catid;

Special thanks to Jay's Outlook MVP from Visual C# Community for the guidance.

        public Guid fmtid;

      public Guid dbcc_classguid;

      public Guid dbcc_classguid;

    Public dbcc_classguid As GUID

        public Guid GUID;                                            // Guid of this junction point

    public Guid    DomainGuid;

    public Guid DiskId;

        public Guid DomainGuid;

     public GUID SiteObjectGuid;

     public GUID ComputerObjectGuid;

     public GUID ServerObjectGuid;

     public GUID NtdsDsaObjectGuid;

       public Guid clsid;

    Public clsid As Guid

   public Guid guidPropSet;

    '    The globally unique identifier (GUID) that identifies the property set.

    Public guidPropSet As Guid

public class GuidClass

    public Guid TheGuid;

Structure GuidClass

   Public Guid TheGuid

Instead of this, you could choose to define such a parameter as an array of System.Guids and only ever use the first element.

public class GuidClass

    public Guid TheGuid;

Structure GuidClass

   Public Guid TheGuid

Instead of this, you could choose to define such a parameter as an array of System.Guids and only ever use the first element.

     public Guid AppId;

pApplicationId: a string that supplies a vendor-defined token. DIFxAPI uses this token to associate an application with the driver package. This token should be a unique application-specific value, such as a GUID. DIFxAPI does not enforce uniqueness among the tokens. If a caller supplies an INSTALLERINFO structure that specifies an association between an application and a driver package, this member must not be NULL or supply an empty string.

http://msdn.microsoft.com/library/default.asp?url=/library/en-us/cpguide/html/cpcondefaultmarshalingforstrings.asp

    [MarshalAs(UnmanagedType.LPStruct)]  public Guid pIID;

Change public Guid pIID to IntPtr and marshal your guid directly to an allocated memory block and this struct will work with CoCreateInstanceEx.

    Dim guidItem As Guid

   public Guid guidItem;

    public Guid clsid;

     Public clsid As Guid

    public Guid PartitionType;

    public Guid PartitionId;

  public Guid PowerSetting;

    public Guid fmtid;

  public Guid clsid;

    public  Guid     interfaceClassGuid;

    Public interfaceClassGuid As Guid

interfaceClassGuid, GUID of the device interface class.

   public Guid classGuid;

    Public classGuid As Guid

classGuid, GUID of the device interface class.

    /// FMTID (GUID) of the current property set, specified when the property set was initially created.

    public Guid fmtid;

    /// CLSID (GUID) associated with this property set, specified when the property set was initially created

    /// will be Guid.Empty.

    public Guid clsid;

        public Guid SubFormat;      

    Dim SubFormat As Guid

    Dim SubFormat As Guid

     public Guid IPDeviceID;

    public Guid interfaceGuid;

        Public interfaceGuid As Guid

    internal struct GuidStruct

        internal GuidStruct Initialize()

        internal GuidStruct Initialize(string guid)

        ConvertirToGuidStruct(guid);

        internal void ConvertToGuidStruct(string guid)

        string[] guidTab = guid.Split(new char[] { ':', '-' });

        if (guidTab.Length == 5)

            this.Data1 = Convert.ToUInt32(guidTab[0], 16);

            this.Data2 = Convert.ToUInt16(guidTab[1], 16);

            this.Data3 = Convert.ToUInt16(guidTab[2], 16);

            byte[] data4Part1 = BitConverter.GetBytes(Convert.ToInt16(guidTab[3], 16));

            byte[] data4Part2 = BitConverter.GetBytes(Convert.ToInt64(guidTab[4], 16));

        string guid;

        guid = Data1.ToString("x").PadLeft(8, '0');

        guid += "-" + Data2.ToString("x").PadLeft(4, '0');

        guid += "-" + Data3.ToString("x").PadLeft(4, '0');

        guid += "-" + BitConverter.ToInt16(new byte[] { Data4[0], Data4[1] }, 0).ToString("x");

        guid += "-" + BitConverter.ToInt64(new byte[] { Data4[2], Data4[3], Data4[4], Data4[5], Data4[6], Data4[7], 0, 0 }, 0).ToString("x");

        return guid;

Structure _GUID

private static extern uint BluetoothEnumerateInstalledServices(IntPtr hRadio, ref Bluetooth_Device_Info pbtdi, ref uint pcServices,  Guid[] pGuidServices);

private static extern uint BluetoothSetServiceState(IntPtr hRadio, ref BLUETOOTH_DEVICE_INFO pbtdi, ref   Guid pGuidService, DwServiceFlags dwServiceFlags);

    [Guid("6B3A1F0C-C382-40d6-AA13-33B0AB46EEAA")]

        protected const string guid = "{6B3A1F0C-C382-40d6-AA13-33B0AB46EEAA}";

                rk.SetValue(guid.ToString(), "BatchResults shell extension");

                // Set "Folder\\shellex\\ContextMenuHandlers\\BatchResults" regkey to my guid

                rk.SetValue("", guid.ToString());

                rk.DeleteValue(guid);

///     at least as large as the actual length of the text; you can thus always use it to guide buffer allocation. This

ms-help://MS.VSCC.2003/MS.MSDNQTR.2003FEB.1033/cpguide/html/cpcondefaultmarshalingforstrings.htm

        ref Guid PowerSettingGuid,

    static Guid GUID_BATTERY_PERCENTAGE_REMAINING = new Guid("A7AD8041-B45A-4CAE-87A3-EECBB468A9E1");

    static Guid GUID_MONITOR_POWER_ON = new Guid(0x02731015, 0x4510, 0x4526, 0x99, 0xE6, 0xE5, 0xA1, 0x7E, 0xBD, 0x1A, 0xEA);

    static Guid GUID_ACDC_POWER_SOURCE = new Guid(0x5D3E9A59, 0xE9D5, 0x4B00, 0xA6, 0xBD, 0xFF, 0x34, 0xFF, 0x51, 0x65, 0x48);

    static Guid GUID_POWERSCHEME_PERSONALITY = new Guid(0x245D8541, 0x3943, 0x4422, 0xB0, 0x25, 0x13, 0xA7, 0x84, 0xF6, 0x79, 0xB7);

    static Guid GUID_MAX_POWER_SAVINGS = new Guid(0xA1841308, 0x3541, 0x4FAB, 0xBC, 0x81, 0xF7, 0x15, 0x56, 0xF2, 0x0B, 0x4A);

    static Guid GUID_MIN_POWER_SAVINGS = new Guid(0x8C5E7FDA, 0xE8BF, 0x4A96, 0x9A, 0x85, 0xA6, 0xE2, 0x3A, 0x8C, 0x63, 0x5C);

    static Guid GUID_TYPICAL_POWER_SAVINGS = new Guid(0x381B4222, 0xF694, 0x41F0, 0x96, 0x85, 0xFF, 0x5B, 0xB2, 0x60, 0xDF, 0x2E);

        public Guid PowerSetting;

        public Guid PowerSetting;

        ref GUID_ACDC_POWER_SOURCE,

        ref GUID_BATTERY_PERCENTAGE_REMAINING,

        ref GUID_MONITOR_POWER_ON,

        ref GUID_POWERSCHEME_PERSONALITY,

        if (ps.PowerSetting == GUID_POWERSCHEME_PERSONALITY &&

            ps.DataLength == Marshal.SizeOf(typeof(Guid)))

            Guid newPersonality =

            (Guid)Marshal.PtrToStructure(pData, typeof(Guid));

            if (newPersonality == GUID_MAX_POWER_SAVINGS)

            else if (newPersonality == GUID_MIN_POWER_SAVINGS)

            else if (newPersonality == GUID_TYPICAL_POWER_SAVINGS)

        else if (ps.PowerSetting == GUID_ACDC_POWER_SOURCE &&

public static extern uint WlanConnect(IntPtr hClientHandle,ref Guid pInterfaceGuid,ref WLAN_CONNECTION_PARAMETERS pConnectionParameters,IntPtr pReserved);

                         ByRef pInterfaceGuid As Guid, _

WlanConnect(ClientHandle,ref pInterfaceGuid,ref wlanConnectionParameters ,new IntPtr());

WlanConnect(ClientHandle, pInterfaceGuid, wlanConnectionParameters, IntPtr.Zero)

public static extern uint WlanDeleteProfile(IntPtr hClientHandle,ref Guid pInterfaceGuid,string strProfileName,IntPtr pReserved);

public static extern uint  WlanDisconnect(IntPtr hClientHandle,ref Guid pInterfaceGuid,IntPtr pReserved);

public static extern uint WlanGetAvailableNetworkList(IntPtr hClientHandle, ref Guid pInterfaceGuid, uint dwFlags, IntPtr pReserved, ref IntPtr ppAvailableNetworkList);

     Public Shared Function WlanGetAvailableNetworkList(ByVal hClientHandle As IntPtr, ByRef pInterfaceGuid As Guid, ByVal dwFlags As UInteger, ByVal pReserved As IntPtr, ByRef ppAvailableNetworkList As IntPtr) As UInteger

Guid pInterfaceGuid = ((WLAN_INTERFACE_INFO)wlanInterfaceInfoList.InterfaceInfo[0]).InterfaceGuid;

WlanGetAvailableNetworkList(ClientHandle, ref pInterfaceGuid, WLAN_AVAILABLE_NETWORK_INCLUDE_ALL_MANUAL_HIDDEN_PROFILES, new  IntPtr(), ref  ppAvailableNetworkList);

    [In, MarshalAs(UnmanagedType.LPStruct)] Guid interfaceGuid,

WlanGetProfileList(ClientHandle, pInterfaceGuid, IntPtr.Zero, out ppProfileList);

public static extern uint WlanGetProfileList(IntPtr hClientHandle,ref Guid pInterfaceGuid,IntPtr pReserved, ref IntPtr ppProfileList);

WlanGetProfileList(ClientHandle, ref pInterfaceGuid, new IntPtr(), ref ppProfileList);

        [In] ref Guid pInterfaceGuid,

    <[In]> ByRef pInterfaceGuid As Guid, ByVal OpCode As WLAN_INTF_OPCODE, _

        Guid guid;

            guid = infoList.InterfaceInfo[i].InterfaceGuid;

            if (WlanQueryInterface(handle, ref guid, WLAN_INTF_OPCODE.wlan_intf_opcode_current_connection, IntPtr.Zero, out dataSize, ref ptr, IntPtr.Zero) != 0)

     Dim guid As Guid

         guid = infoList.InterfaceInfo(i).InterfaceGuid

         If WlanQueryInterface(handle, guid, WLAN_INTF_OPCODE.wlan_intf_opcode_current_connection, IntPtr.Zero, dataSize, ptr, _

public static extern uint WlanScan(IntPtr hClientHandle,ref Guid pInterfaceGuid,IntPtr pDot11Ssid,IntPtr pIeData,IntPtr pReserved);

Public Shared Function WlanScan(ByVal hClientHandle As IntPtr, ByRef pInterfaceGuid As Guid, ByVal pDot11Ssid As IntPtr, ByVal pIeData As IntPtr, ByVal pReserved As IntPtr) As UInteger

      Guid g;

      g = infoList.InterfaceInfo[i].InterfaceGuid;

public static extern uint WlanSetInterface(IntPtr hClientHandle,ref Guid pInterfaceGuid,WLAN_INTF_OPCODE OpCode,uint dwDataSize,ref object obj ,IntPtr pReserved);

public static extern uint WlanSetProfilePosition(IntPtr hClientHandle,ref Guid pInterfaceGuid,string strProfileName,uint dwPosition,IntPtr pReserved);

public static extern uint WlanSetProfileList(IntPtr hClientHandle,ref Guid pInterfaceGuid,uint dwItems,string[] strProfileNames,IntPtr pReserved);

        [In] ref Guid iid,

Public Declare Ansi Sub DtcGetTransactionManager Lib "xolehlp.dll" (ByVal hostName As String, ByVal tmName As String, ByVal iid As Guid, ByVal dwReserved1 As Integer, ByVal wReserved2 As Short, ByVal pvReserved As Integer, ByRef ppv As Integer)

    Guid clsid;

      // String-ized GUID as returned by IIDFromString().

    internal static extern void DsFreeSchemaGuidMap(

        IntPtr pGuidMap);

Declare Function DsFreeSchemaGuidMap Lib "ntdsapi.dll" (TODO) As TODO

        result = DsMapSchemaGuids(phDS, (uint)myGuids.Length, myGuids, out guidMap);

        DsFreeSchemaGuidMap(guidMap);

    public struct GUID

        public GUID SiteObjectGuid;

        public GUID ComputerObjectGuid;

        public GUID ServerObjectGuid;

        public GUID NtdsDsaObjectGuid;

    internal static extern uint DsMapSchemaGuids(

        uint cGuids,

        Guid[] rGuids,

        out IntPtr ppGuidMap);

    Friend Shared Function DsMapSchemaGuids(hDs As IntPtr, cGuids As UInteger, rGuids As Guid(), ByRef ppGuidMap As IntPtr) As UInteger

Requires DsBind, recommend DsUnBind and DsFreeSchemaGuidMap

        IntPtr guidMap = new IntPtr(0);

        Guid[] myGuids = {

        new Guid("{e0fa1e69-9b45-11d0-afdd-00c04fd930c9}"),

        new Guid("{771727b1-31b8-4cdf-ae62-4fe39fadf89e}"),

        new Guid("{d5eb2eb7-be4e-463b-a214-634a44d7392e}"),

        new Guid("{e0fa1e8c-9b45-11d0-afdd-00c04fd930c9}")

        result = DsMapSchemaGuids(phDS, (uint)myGuids.Length, myGuids, out guidMap);

        DS_SCHEMA_GUID_MAP[] guidMapResult = parseGuids(guidMap, myGuids.Length, true);

        for (int i = 0; i < guidMapResult.Length; i++)

            Console.WriteLine("{0} = {1}", myGuids[i], guidMapResult[i].pName);

    internal static extern uint DsMapSchemaGuids(

        uint cGuids,

        Guid[] rGuids,

        out IntPtr ppGuidMap);

    internal static extern void DsFreeSchemaGuidMap(

        IntPtr pGuidMap);

    internal class GUID

    internal struct DS_SCHEMA_GUID_MAP

        internal GUID guid;

        internal uint guidType;

    private static DS_SCHEMA_GUID_MAP[] parseGuids(IntPtr guidMap, int numGuids, bool freePointer)

        int typeSize = Marshal.SizeOf(typeof(DS_SCHEMA_GUID_MAP));

        DS_SCHEMA_GUID_MAP[] schemaMap = new DS_SCHEMA_GUID_MAP[numGuids];

        IntPtr guidPointer = guidMap;

        for (int i = 0; i < numGuids; i++)

        schemaMap[i] = (DS_SCHEMA_GUID_MAP)Marshal.PtrToStructure(

                (long)guidPointer + i * typeSize

                typeof(DS_SCHEMA_GUID_MAP)

        DsFreeSchemaGuidMap(guidPointer);

(http://www.gotdotnet.com/Community/UserSamples/Details.aspx?SampleGuid=f1dd70e4-c212-4a6f-bff7-c82e34c8836f)