function on1() 
{if (!document.images) return; document.a.src = "buttons/novinky2.gif";} 
function on2() 
{if (!document.images) return; document.b.src = "buttons/o-firme2.gif";}
function on3() 
{if (!document.images) return; document.c.src = "buttons/kontakt2.gif";}
function on4() 
{if (!document.images) return; document.d.src = "buttons/prospekty2.gif";}

function off1() 
{if (!document.images) return; document.a.src = "buttons/novinky1.gif";}
function off2() 
{if (!document.images) return; document.b.src = "buttons/o-firme1.gif";}
function off3() 
{if (!document.images) return; document.c.src = "buttons/kontakt1.gif";}
function off4() 
{if (!document.images) return; document.d.src = "buttons/prospekty1.gif";}

var imgslist = new Array(
"buttons/novinky2.gif",
"buttons/o-firme2.gif",
"buttons/kontakt2.gif",
"buttons/prospekty2.gif"); 

var imgs=new Array(); 
for (x=0; x<imgslist.length; x++) 
 if (document.images) 
  {imgs[x]=new Image(); imgs[x].src = imgslist[x];}