var banner = new Array();

    banner[0]='http://img819.imageshack.us/img819/9716/fonfo02.png';
    banner[1]='http://img824.imageshack.us/img824/7508/fonfo03.png';
    banner[2]='http://img834.imageshack.us/img834/8662/fonfo04.png';
    banner[3]='http://img225.imageshack.us/img225/2720/fonfoj.png';
    banner[4]='http://img694.imageshack.us/img694/2402/fonfo05.png';
    banner[5]='http://img835.imageshack.us/img835/6181/fonfo06.png';

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