var banner = new Array();

banner.push('http://img843.imageshack.us/img843/6789/004wd.png');
banner.push('http://img831.imageshack.us/img831/1483/001bt.png');
banner.push('http://img819.imageshack.us/img819/3/002uao.png');
banner.push('http://img8.imageshack.us/img8/4650/003ty.png');

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