Public PrevWndProc As Long
PrevWndProc = SetWindowLong(Me.hwnd, GWL_WNDPROC, AddressOf MessageHandler)

Public Function MessageHandler(ByVal hwnd As Long, ByVal MSG As Long, _
                            ByVal wParam As Long, ByVal lParam As Long) As Long
 
    If MSG = WM_COPYDATA Then
            '.............Auswertung
    End If
 
    'Aufruf des normalen Messagehandlers
    MessageHandler = CallWindowProc(PrevWndProc, hwnd, MSG, wParam, lParam)
End Function

    'Zurücksetzen des MessageHandlers
    SetWindowLong Me.hwnd, GWL_WNDPROC, PrevWndProc