var banner = new Array();

banner[0]='http://img18.imageshack.us/img18/24/sahuh.jpg';
banner[0]='https://i.servimg.com/u/f36/14/46/21/26/top10.jpg';

document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];
setInterval("document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];",5000);