Sub SetProc(ByVal hwnd As Long)
   oldProc = SetWindowLong(hwnd, GWL_WNDPROC, AddressOf NewProc)
End Sub

Sub DelProc(ByVal hwnd As Long)
   SetWindowLong hwnd, GWL_WNDPROC, oldProc
End Sub

Private Function NewProc(ByVal hwnd As Long, ByVal msg As Long, ByVal wParam As _
  Long, ByVal lParam As Long) As Long
 
.....
   NewProc = CallWindowProc(oldProc, hwnd, msg, wParam, lParam)
End Function