How to Change the Windows Start button bitmap

{We'll need several global variables}
var
    Form1: TForm1;
    StartButton : hWnd;
    OldBitmap : THandle;
    NewImage : TPicture;
...
{Now, we put this code in the
OnCreate event of the form:}

procedure TForm1.FormCreate(Sender: TObject) ;
begin
  NewImage:=TPicture.create;
  NewImage.LoadFromFile('C:WindowsCircles.BMP') ;
  StartButton := FindWindowEx
                  (FindWindow(
                     'Shell_TrayWnd', nil),
                      0,'Button', nil) ;
   OldBitmap:=SendMessage(StartButton,
                          BM_SetImage, 0,
                          NewImage.Bitmap.Handle) ;
  end;
...
{And this other in the OnDestroy:}

  procedure TForm1.FormDestroy(Sender: TObject) ;
  begin
   SendMessage(StartButton,BM_SetImage,0,OldBitmap) ;
   NewImage.Free;
  end;