var img = []; // preloading array
var len = (links.length + imgs.length) / 2; // length

var timeBasis = 3; // in seconds 
   // preload images
      for(i=0; i<imgs.length; i++){
         img[i] = new Image();
         img[i].src = imgs[i];
      }

function showAd(){
   if(len%2 == 0){
            document.write('<img src="/images/WebGeneral/shim.gif" alt="" vspace="0" hspace="0" border="0">');
         return false;
      }
   var rand = Math.floor(len*Math.random());
   document.write('<a href="'+links[rand]+'" title="Go to '+links[rand]+'" id="myAd">');
   document.write('<img src="'+img[rand].src+'" alt="Go to '+links[rand]+'" name="myAdImg"></a>');
   setInterval("updateAd()", timeBasis*1000);
}

function updateAd(){
   var r = Math.floor(len*Math.random());
      if(!document.links) return false;
         for(i=0; i<document.links.length; i++){
            if(document.links[i].id == "myAd"){
               if(document.links[i].href != links[r]){
                  document.links[i].href = links[r];
                  document.images['myAdImg'].src = img[r].src;
         } else {
               updateAd();
         }
       }
     }
}