var banner = new Array();

banner[0]='http://i40.servimg.com/u/f40/12/60/42/04/212.png';
banner[1]='http://i40.servimg.com/u/f40/12/60/42/04/5510.png';
banner[2]='http://i40.servimg.com/u/f40/12/60/42/04/cinco11.png';


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