var banner = new Array();

banner[0]='http://i29.tinypic.com/5y8euo.jpg';
banner[1]='http://i30.tinypic.com/2r40hp4.jpg';
banner[2]='http://i27.tinypic.com/2iubc4w.jpg';

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