I'm pretty sure it's not 100% custom. I was just wondering if anyone had seen anything like this before and what it might be (even if it's based on something that's heavily modified)
Actually I poked around for a while and did some research on the source of that page. Many of the tags are consistent with OScommerce tags. I ran it by a buddy of mine as well and he agreed that it's probably OScommerce that has simply been modified to fit the task.