利用Windows API的SetWindowRgn可以做这件事，下面就是一个这方面的例子。 
    Option Explicit 
    Private Declare Function CreatePolygonRgn Lib "gdi32" (lpPoint As POINTAPI, ByVal nCount As Long, ByVal nPolyFillMode As Long) As Long 
    Private Declare Function CreateRectRgn Lib "gdi32" (ByVal x1 As Long, ByVal y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long 
    Private Declare Function CreateRoundRectRgn Lib "gdi32" (ByVal x1 As Long, ByVal y1 As Long, ByVal X2 As Long, ByVal Y2 As Long, ByVal X3 As Long, ByVal Y3 As Long) As Long 
    Private Declare Function CreateEllipticRgn Lib "gdi32" (ByVal x1 As Long, ByVal y1 As Long, ByVal X2 As Long, ByVal Y2 As Long) As Long 
    Private Declare Function CombineRgn Lib "gdi32" (ByVal hDestRgn As Long, ByVal hSrcRgn1 As Long, ByVal hSrcRgn2 As Long, ByVal nCombineMode As Long) As Long 
    Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long 
    Private Declare Function SetWindowRgn Lib "user32" (ByVal hWnd As Long, ByVal hRgn As Long, ByVal bRedraw As Boolean) As Long 
    Private Declare Function SendMessage Lib "user32" Alias "SendMessageA" (ByVal hWnd As Long, ByVal wMsg As Long, ByVal wParam As Long, lParam As Any) As Long 
    Private Declare Function ReleaseCapture Lib "user32" () As Long 
    Private Type POINTAPI 
     X As Long 
     Y As Long 
    End Type 
    Private Const RGN_AND = 1 
    Private Const RGN_COPY = 5 
    Private Const RGN_DIFF = 4 
    Private Const RGN_OR = 2 
    Private Const RGN_XOR = 3 
    Private Function CreateFormRegion() As Long 
     Dim ResultRegion As Long, HolderRegion As Long, ObjectRegion As Long, nRet As Long 
     Dim PolyPoints() As POINTAPI 
     ResultRegion = CreateRectRgn(0, 0, 0, 0) 
     HolderRegion = CreateRectRgn(0, 0, 0, 0) 
     
     
    '!Shaped Form Region Definition 
    '!3,16,105,423,328,0,0,1 
     ObjectRegion = CreateEllipticRgn(105 * 12 / Screen.TwipsPerPixelX, 16 * 12 / Screen.TwipsPerPixelY, 423 * 12 / Screen.TwipsPerPixelX, 328 * 12 / Screen.TwipsPerPixelY) 
     nRet = CombineRgn(ResultRegion, ObjectRegion, ObjectRegion, RGN_COPY) 
     DeleteObject ObjectRegion 
     CreateFormRegion = ResultRegion 
    End Function 
     
    Private Sub Form_Load() 
     Dim nRet As Long 
     nRet = SetWindowRgn(Me.hWnd, CreateFormRegion, True) 
     'If the above two lines are modified or moved a second copy of 
     'them may be added again if the form is later Modified by VBSFC. 
    End Sub 
     
    Private Sub Form_MouseDown(Button As Integer, Shift As Integer, X As Single, Y As Single) 
    'Next two lines enable window drag from anywhere on form. Remove them 
    'to allow window drag from title bar only. 
     ReleaseCapture 
     SendMessage Me.hWnd, &HA1, 2, 0& 
    End Sub 
<END>
