aktOb="a"
  
   on = new Image();       on.src = "obrazy/menu/ml-tl_dole.gif";
   off = new Image();      off.src = "obrazy/menu/ml-tl.gif";
   akt = new Image();      akt.src = "obrazy/menu/ml-tl_hore.gif";

   function imgOn(imgName)
     {
       document.images[imgName].src = on.src;
     }
  	
   function imgOff(imgName) 
     {
       if (aktOb!=imgName)
         document.images[imgName].src = off.src; 
        else
         document.images[imgName].src = akt.src; 
     }

   function imgClick(imgName)
     {
       document.images[aktOb].src = off.src;
       document.images[imgName].src = akt.src;
       aktOb=imgName;
     }