var banner = new Array();

banner[0]='http://img64.imageshack.us/img64/3489/bd4p.png';
banner[1]='http://img823.imageshack.us/img823/5319/bd5h.png';
banner[2]='http://img42.imageshack.us/img42/5307/bd6.png';

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