var banner = new Array();

banner[0]='http://img408.imageshack.us/img408/6384/sinttulo130.jpg';
banner[1]='http://img249.imageshack.us/img249/5234/sinttulo12x.jpg';
banner[2]='http://img840.imageshack.us/img840/8145/sinttulo110.jpg';
banner[3]='http://img408.imageshack.us/img408/6384/sinttulo130.jpg';

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