pinvoke.net: Edit: kernel32.GetNativeSystemInfo

@msdn=http://msdn.microsoft.com/en-us/library/ms724340(VS.85).aspx
@pinvoke=http://pinvoke.net/$$$.htm

Summary: Returns os info. This api can be used in a x86 process to determine if the os supports 64bit. This api is only supported on XP and higher. On lower os versions use Kernel32.GetSystemInfo.

!!!!C# Signature:
 [DllImport("kernel32.dll")]
 internal static extern void GetNativeSystemInfo(ref SYSTEM_INFO lpSystemInfo);
!!!!VB Signature:
 Private Declare Sub GetNativeSystemInfo Lib "kernel32" (<MarshalAs(UnmanagedType.Struct)> ByRef lpSystemInfo As SYSTEM_INFO)
!!!!User-Defined Types:
[SYSTEM_INFO]

!!!!Alternative Unmanaged API:
Kernel32.GetSystemInfo

!!!!Notes:
This sample will determine is the os supports 64bit.

!!!!Tips & Tricks:
Please add some!

!!!!Sample Code:
    public enum Platform
    {
      X86,
      X64,
      IA64,
      Unknown
    }

internal const ushort PROCESSOR_ARCHITECTURE_INTEL = 0;
    internal const ushort PROCESSOR_ARCHITECTURE_IA64 = 6;
    internal const ushort PROCESSOR_ARCHITECTURE_AMD64 = 9;
    internal const ushort PROCESSOR_ARCHITECTURE_UNKNOWN = 0xFFFF;

[StructLayout(LayoutKind.Sequential)]
    internal struct SYSTEM_INFO
    {
      public ushort wProcessorArchitecture;
      public ushort wReserved;
      public uint dwPageSize;
      public IntPtr lpMinimumApplicationAddress;
      public IntPtr lpMaximumApplicationAddress;
      public UIntPtr dwActiveProcessorMask;
      public uint dwNumberOfProcessors;
      public uint dwProcessorType;
      public uint dwAllocationGranularity;
      public ushort wProcessorLevel;
      public ushort wProcessorRevision;
    };

[DllImport("kernel32.dll")]
    internal static extern void GetNativeSystemInfo(ref SYSTEM_INFO lpSystemInfo);

[DllImport("kernel32.dll")]
    internal static extern void GetSystemInfo(ref SYSTEM_INFO lpSystemInfo);

public static Platform GetPlatform()
    {
      SYSTEM_INFO sysInfo = new SYSTEM_INFO();

if(System.Environment.OSVersion.Version.Major > 5 ||
        (System.Environment.OSVersion.Version.Major == 5 && System.Environment.OSVersion.Version.Minor >= 1))
      {
        GetNativeSystemInfo(ref sysInfo);
      }
      else
      {
        GetSystemInfo(ref sysInfo);
      }

switch(sysInfo.wProcessorArchitecture)
      {
        case PROCESSOR_ARCHITECTURE_IA64:
          return Platform.IA64;

case PROCESSOR_ARCHITECTURE_AMD64:
          return Platform.X64;

case PROCESSOR_ARCHITECTURE_INTEL:
          return Platform.X86;

default:
          return Platform.Unknown;
      }
    }

Documentation: GetNativeSystemInfo@msdn on MSDN