var banner = new Array();

banner[0]='http://www.effectsfx.com/eyy/1.jpg';
banner[1]='http://www.effectsfx.com/eyy/2.jpg';
banner[2]='http://www.effectsfx.com/eyy/3.jpg';
banner[3]='http://www.effectsfx.com/eyy/4.jpg';
banner[4]='http://www.effectsfx.com/eyy/5.jpg';

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