{Скрыть}
   procedure TForm1.Button1Click(Sender: TObject); 
   begin 
     ShowWindow(FindWindow(nil,'Program Manager'),SW_HIDE); 
   end;

   {Появить}
   procedure TForm1.Button2Click(Sender: TObject); 
   begin 
     ShowWindow(FindWindow(nil,'Program Manager'),SW_SHOW); 
   end;
	             		

Источник: www.sources.ru