怎样响应窗体单击标题栏的事件？

'分二步
'一、新建一个模块，复制下面代码
Option Explicit
Private Declare Function CallWindowProc _
Lib "USER32" Alias "CallWindowProcA" _
(ByVal lpPrevWndFunc As Long, _
ByVal hWnd As Long, _
ByVal Msg As Long, _
ByVal wParam As Long, _
ByVal lParam As Long) As Long

Private Declare Function SetWindowLong _
Lib "USER32" Alias "SetWindowLongA" _
(ByVal hWnd As Long, _
ByVal nIndex As Long, _
ByVal dwNewLong As Long) As Long

Private Const GWL_WNDPROC = -4

Global lpPrevWndProc As Long

Public Sub Hook(ByVal hWnd As Long)
lpPrevWndProc = SetWindowLong(hWnd, GWL_WNDPROC, _
AddressOf WindowProc)
End Sub

Public Sub UnHook(ByVal hWnd As Long)
Dim lngReturnvalue As Long
lngReturnvalue = SetWindowLong(hWnd, GWL_WNDPROC, lpPrevWndP