var banner = new Array();

banner[0]='https://i.servimg.com/u/f66/12/46/70/00/gatas10.png';
banner[1]='http://img684.imageshack.us/img684/9596/gatatop1002.png';
banner[2]='http://img442.imageshack.us/img442/1444/gatas10otop.png';

document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];
setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",9000);