function getAd()
{
   var image = 'gobalto1.jpg'; 
   var randomnumber=Math.floor(Math.random()*2);
   if(randomnumber > 0) image = 'gobalto2.jpg';
   var adlayer = document.getElementById('gobaltoad');
   var adhtml = '<a href="http://www.gobalto.com/signup"><img src="'+image+'" border="0"></a>';
   adlayer.innerHTML = adhtml;   
   adlayer.style.visibility="visible";
}

window.onload=getAd;