var banner = new Array();

banner[0]='http://i40.tinypic.com/wjyvzp.png';
banner[1]='http://i40.tinypic.com/wjyvzp.png';
banner[2]='http://i52.tinypic.com/2af9x07.png';
banner[3]='http://i55.tinypic.com/107mn9d.png';

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)];",8000);