Просто этот код надо вставить в обработку событий формы...
Код: Выделить всё
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 SetWindowRgn Lib "user32" _
(ByVal hWnd As Long, _
ByVal hRgn As Long, ByVal bRedraw As Boolean) As Long
'--------------------------------------------------
Private Sub Form_Load()
SetWindowRgn hWnd, _
CreateEllipticRgn(0, 0, 300, 200), True
End Sub