var banner = new Array();

banner[0]='https://i.servimg.com/u/f68/14/88/38/33/alianz10.jpg';
banner[1]='http://img62.imageshack.us/img62/2605/alianz12.jpg';
banner[2]='http://img189.imageshack.us/img189/4354/alianz13.jpg';
banner[3]='http://img535.imageshack.us/img535/1935/alianz14.jpg';
banner[4]='http://img203.imageshack.us/img203/575/alianz15.jpg';

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

setInterval("document.getElementById('logo').firstChild.src= banner[Math.floor(Math.random()*banner.length)];",3000);