var banner = new Array();

banner[0]='http://img707.imageshack.us/img707/2527/bannervff.jpg';
banner[1]='http://img42.imageshack.us/img42/1613/bannercorvo.png';
banner[2]='http://img39.imageshack.us/img39/5867/bannerelefante.png';
banner[3]='http://img189.imageshack.us/img189/521/bannerfiguras.png';

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