This using this code. You can add as many rotating banners that you want.
Code:
<!-- Begin rotating ad code -->
<script language="Javascript"><!--
function image() {
};
image = new image();
number = 0;
// imageArray
image[number++] = "<a href='http://www.yoursite.net/forum/payments.php'><img src='http://www.yoursite.net/forum/sponsors/donatebanner.gif' border='0'></a>"
image[number++] = "<a href='http://www.hikersupply.com'><img src='http://www.yoursite.net/forum/sponsors/hikersupply.gif' border='0'></a>"
image[number++] = "<a href='http://www.modelt.net'><img src='http://www.yoursite.net/forum/sponsors/modeltbanner.gif' border='0'></a>"
image[number++] = "<a href='http://appalachiantrailservices.com/'><img src='http://www.yoursite.net/forum/sponsors/atservicesbanner.gif' border='0'></a>"
image[number++] = "<a href='http://www.thepacka.com/'><img src='http://www.yoursite.net/forum/sponsors/cedartreebanner.gif' border='0'></a>"
// Carry on adding images - as many as you want
increment = Math.floor(Math.random() * number);
document.write(image[increment]);
//-->
</script>
<!-- End rotating ad code -->