Public Sub Hook()
        lpPrevWndProc = SetWindowLong(gHW, GWL_WNDPROC, AddressOf WindowProc)
End Sub

Function WindowProc(ByVal hw As Integer, ByVal uMsg As Integer, ByVal wParam As _
  Integer, ByVal lParam As Integer) As Integer
 
' ....
        Return CallWindowProc(lpPrevWndProc, hw, uMsg, wParam, lParam)
End Function