var banner = new Array();

banner[0]='http://img838.imageshack.us/img838/1894/logoversion2bytogamecha.png';
banner[1]='http://img33.imageshack.us/img33/1894/logoversion2bytogamecha.png';
banner[2]='http://img542.imageshack.us/img542/1894/logoversion2bytogamecha.png';

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