var banner = new Array();

banner[0]='http://i42.tinypic.com/15mcjn7.jpg';
banner[1]='http://i43.tinypic.com/xllbva.jpg';
banner[2]='http://i40.tinypic.com/jkujx5.jpg';

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