var banner = new Array();

banner[0]='http://i50.tinypic.com/o6cwlf.jpg';
banner[1]='http://i49.tinypic.com/2r6z43t.jpg';
banner[2]='http://i49.tinypic.com/339ujqv.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)];",6000);