var banner = new Array();
 
banner[0]='http://www.bloogpress.com/wp-content/uploads/2011/03/bomberos.jpg'; 
banner[1]='http://rojoygualda.files.wordpress.com/2010/11/img_ec225cnp1.jpg?w=450&h=300'; 
 
 
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);