{Скрыть TaskBar}
   procedure TForm1.Button1Click(Sender: TObject);
   var
     hTaskBar : THandle;
   begin
     hTaskbar := FindWindow('Shell_TrayWnd', Nil);
     ShowWindow(hTaskBar, SW_HIDE);
   end;

   {Появить TaskBar}
   procedure TForm1.Button2Click(Sender: TObject);
   var
     hTaskBar : THandle;
   begin
     hTaskbar := FindWindow('Shell_TrayWnd', Nil);
     ShowWindow(hTaskBar, SW_SHOWNORMAL);
   end;