var banner = new Array();

banner[0]='https://i.servimg.com/u/f62/15/82/45/88/sem_ta10.jpg';
banner[1]='http://img830.imageshack.us/img830/3420/pokemonredetvdois.png';

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