Private Sub Form_Click()
End
End Sub

Private Sub Form_Load()
Dim h,d As Long
Dim scrw,scrh As Long
scrw = Me.Width / Screen.TwipsPerPixelX
scrh = Me.Height / Screen.TwipsPerPixelY
h = CreateEllipticRgn(0,scrw,scrh)
d = SetWindowRgn(Me.hWnd,h,True)
End Sub

Option Explicit

Public Declare Function CreateEllipticRgn Lib "gdi32" (ByVal X1 As Long,ByVal Y1 As Long,ByVal X2 As Long,ByVal Y2 As Long) As Long
'CreateEllipticRgn http://baike.baidu.com/view/2034860.htm
Public Declare Function SetWindowRgn Lib "user32" (ByVal hWnd As Long,ByVal hRgn As Long,ByVal bRedraw As Boolean) As Long
'SetWindowRgn http://baike.baidu.com/view/1559429.htm