C# Signature:

[ComImport,
Guid("56fdf342-fd6d-11d0-958a-006097c9a090"),
InterfaceType(ComInterfaceType.InterfaceIsIUnknown)]
public interface ITaskbarList
{
     /// <summary>
     /// Initializes the taskbar list object. This method must be called before any other ITaskbarList methods can be called.
     /// </summary>
     void HrInit();

     /// <summary>
     /// Adds an item to the taskbar.
     /// </summary>
     /// <param name="hWnd">A handle to the window to be added to the taskbar.</param>
     void AddTab([In] IntPtr hWnd);

     /// <summary>
     /// Deletes an item from the taskbar.
     /// </summary>
     /// <param name="hWnd">A handle to the window to be deleted from the taskbar.</param>
     void DeleteTab([In] IntPtr hWnd);

     /// <summary>
     /// Activates an item on the taskbar. The window is not actually activated; the window's item on the taskbar is merely displayed as active.
     /// </summary>
     /// <param name="hWnd">A handle to the window on the taskbar to be displayed as active.</param>
     void ActivateTab([In] IntPtr hWnd);

     /// <summary>
     /// Marks a taskbar item as active but does not visually activate it.
     /// </summary>
     /// <param name="hWnd">A handle to the window to be marked as active.</param>
     void SetActiveAlt([In] IntPtr hWnd);
}

[ComImport]
[Guid("56fdf344-fd6d-11d0-958a-006097c9a090")]
public class CoTaskbarList
{
}

VB Signature:

Declare Function ITaskbarList Lib "shell32.dll" (TODO) As TODO

VB.NET full Implementation:

Since I wanted this to work on x64 and x86 Plattforms I used the IntPtr based approach.

It works perfect using Windows7 (64) - in WinXP the Taskbar-Items tend to reappear after a while after hiding them.

Don't forget to Import System.Runtime.CompilerServices and System.Runtime.InteropServices

    <ComImport, TypeLibType(CShort(2)), Guid("56FDF344-FD6D-11D0-958A-006097C9A090"), ClassInterface(CShort(0))> _
    Public Class TaskbarListClass
    Implements ITaskbarList, TaskbarList
    ' Methods
    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Public Sub New()
    End Sub

    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Public Overridable Sub ActivateTab(<[In]> ByVal hwnd As IntPtr) Implements ITaskbarList.ActivateTab
    End Sub

    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Public Overridable Sub AddTab(<[In]> ByVal hwnd As IntPtr) Implements ITaskbarList.AddTab
    End Sub

    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Public Overridable Sub DeleteTab(<[In]> ByVal hwnd As IntPtr) Implements ITaskbarList.DeleteTab
    End Sub

    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Public Overridable Sub HrInit() Implements ITaskbarList.HrInit
    End Sub

    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Public Overridable Sub SetActivateAlt(<[In]> ByVal hwnd As IntPtr) Implements ITaskbarList.SetActivateAlt
        End Sub
    End Class

    <ComImport, Guid("56FDF342-FD6D-11D0-958A-006097C9A090"), CoClass(GetType(TaskbarListClass))> _
    Public Interface TaskbarList
    Inherits ITaskbarList
    End Interface

    <ComImport, InterfaceType(CShort(1)), Guid("56FDF342-FD6D-11D0-958A-006097C9A090")> _
    Public Interface ITaskbarList
    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Sub HrInit()
    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Sub AddTab(<[In]> ByVal hwnd As IntPtr)
    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Sub DeleteTab(<[In]> ByVal hwnd As IntPtr)
    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Sub ActivateTab(<[In]> ByVal hwnd As IntPtr)
    <MethodImpl(MethodImplOptions.InternalCall, MethodCodeType:=MethodCodeType.Runtime)> _
    Sub SetActivateAlt(<[In]> ByVal hwnd As IntPtr)
    End Interface

User-Defined Types:

None.

Alternative Managed API:

http://code.msdn.microsoft.com/WindowsAPICodePack

Notes:

None.

Tips & Tricks:

Please add some!

Sample Code:

IntPtr windowHandle = ...;
var taskbarList = (ITaskbarList) new CoTaskbarList();
taskbarList.HrInit();
taskbarList.DeleteTab(windowHandle);

http://msdn.microsoft.com/en-us/library/bb774652(VS.85).aspx