The SetWindowStyle subroutine makes a lot of this easy.

The code was modified by Peter Chamberlin UK to allow the ShowInTaskbar property to be altered as well (requires window hide/show).

' Set or clear a style or extended style value.
Private Sub SetWindowStyle(ByVal hwnd As Long, ByVal _
    extended_style As Boolean, ByVal style_value As Long, _
    ByVal new_value As Boolean, ByVal brefresh As Boolean)
Dim style_type As Long
Dim style As Long
   
    If extended_style Then
        style_type = GWL_EXSTYLE
    Else
        style_type = GWL_STYLE
    End If

    ' Get the current style.
    style = GetWindowLong(hwnd, style_type)

    ' Add or remove the indicated value.
    If new_value Then
        style = style Or style_value
    Else
        style = style And Not style_value
    End If

    ' Hide Window if Changing ShowInTaskBar
    If brefresh Then
        ShowWindow hwnd, SW_HIDE
    End If

    ' Set the style.
    SetWindowLong hwnd, style_type, style

    ' Show Window if Changing ShowInTaskBar
    If brefresh Then
        ShowWindow hwnd, SW_SHOW
    End If

    ' Make the window redraw.
    SetWindowPos hwnd, 0, 0, 0, 0, 0, _
        SWP_FRAMECHANGED Or _
        SWP_NOMOVE Or _
        SWP_NOSIZE Or _
        SWP_NOZORDER
End Sub