var banner = new Array();

banner[0]='https://i791.photobucket.com/albums/yy199/Nicolas0402/ForoImagen.jpg';
banner[1]='http://img821.imageshack.us/img821/607/maschik.jpg';
banner[2]='http://img819.imageshack.us/img819/6536/dreykans.jpg';

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