var banner = new Array();

banner[0]='http://i20.servimg.com/u/f20/15/70/13/89/nono211.png';
banner[1]='http://i20.servimg.com/u/f20/15/70/13/89/nono310.png';
banner[2]='http://i20.servimg.com/u/f20/15/70/13/89/nono311.png';

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