Code:
procedure TForm1.FormShow(Sender: TObject) ;
var
   r : TRect;
begin
   Borderstyle := bsNone;
   SystemParametersInfo
      (SPI_GETWORKAREA, 0, @r,0) ;
   SetBounds
     (r.Left, r.Top, r.Right-r.Left, r.Bottom-r.Top) ;
end;