My god, what a hideous website.
I think what you need for this is JS's window.setInterval() function. A basic version:
It assumes there's an image the the id 'banner' and it'll change the src attribute every 2 seconds. If you want the links at the bottom too, that can easily be incorporated.
var images = ['img1.gif','img2.gif','img3.gif','img4.gif'];
var counter = 0;
if (counter == 4) counter = 0;