Private Sub Form_Load()

Dim rgn As Long

Dim wid As Single

Dim hgt As Single

If WindowState = vbMinimized Then Exit Sub

' Create the elliptical region.

wid = ScaleX(Width, vbTwips, vbPixels)

hgt = ScaleY(Height, vbTwips, vbPixels)

rgn = CreateEllipticRgn(0, 0, wid, hgt)

' Restrict the window to the region.

SetWindowRgn hWnd, rgn, True

'DeleteObject rgn

End Sub

В модуле написать

Option Explicit

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 Long) As Long

Private Declare Function DeleteObject Lib "gdi32" (ByVal hObject As Long) As Long