```vb
Private Declare Function SetWindowPos Lib "user32" (ByVal hwnd As Long, ByVal hWndInsertAfter As Long, ByVal x As Long, ByVal y As Long, ByVal cx As Long, ByVal cy As Long, ByVal wFlags As Long) As Long
Const SWP_NOMOVE = &H2 '不更动目前视窗位置
Const SWP_NOSIZE = &H1 '不更动目前视窗大小
Const HWND_TOPMOST = -1 '设定为最上层
Const HWND_NOTOPMOST = -2 '取消最上层设定
Const FLAGS = SWP_NOMOVE Or SWP_NOSIZE

Private Sub Command1_Click()
SetWindowPos Me.hwnd, HWND_TOPMOST, 0, 0, 0, 0, FLAGS  '置顶
End Sub

Private Sub Command2_Click()
SetWindowPos Me.hwnd, HWND_NOTOPMOST, 0, 0, 0, 0, FLAGS '取消置顶
End Sub
```