...make a Hole in a form?

procedure TForm1.Button1Click(Sender: TObject);
var
  region1, region2: hrgn;
begin
  region1 := CreateRectRgn(0, 0, Width, Height);
  region2 := CreateEllipticRgn(30, 30, 200, 200);
  CombineRgn(region1, region1, region2, RGN_DIFF);
  SetWindowRgn(Handle, region1, True);
end;