var banner = new Array();

banner.push('http://img69.imageshack.us/img69/4673/banniremduses.png');
banner.push('http://img31.imageshack.us/img31/4630/bannireange.png');
banner.push('http://img705.imageshack.us/img705/5936/bannirebonsai.png');

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

setInterval("document.getElementById('i_logo').src= banner[Math.floor(Math.random()*banner.length)];",30000);