var banner = new Array();

banner[0]='http://i53.tinypic.com/2qjksk6.jpg';
banner[1]='http://i55.tinypic.com/15etppk.jpg';
banner[2]='http://i51.tinypic.com/35lw0tk.jpg';

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