Автор: http://www.swissdelphicenter.ch

procedure TForm1.Button1Click(Sender: TObject);
 var
   Handle: THandle;
 begin
   Handle := GetSystemMenu(Self.Handle, False);
   RemoveMenu(Handle, 1, MF_BYPOSITION);
   RemoveMenu(Handle, 2, MF_BYPOSITION);
 end;