var banner = new Array();

banner[0]='http://img201.imageshack.us/img201/425/bannergpt4.jpg'; banner[1]='http://img714.imageshack.us/img714/4232/bannergpt2.jpg'; banner[2]='http://img221.imageshack.us/img221/1310/bannergpt3.jpg'; 

document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];
setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",5000);