var banner = new Array();

banner[0]='http://i55.tinypic.com/34xpeuc.jpg';
banner[1]='http://i55.tinypic.com/2jab2jd.jpg';
banner[2]='http://i53.tinypic.com/2upa7gk.jpg';
document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];