I agere with what Tekoneiric is saying on the setup, AmiTCP has problems doing DHCP connects. I would add though that you need to do the same for your roommates PC(s), set it with a static IP to the router so you know there are no conflicting IP issues.
Knowing the router model might help us help you. I've used a LinkSYS BSRF41 to connect 3 PCs, 2 Amigas and a Power MAC. Now using a Linux server, I built for less than the cost of the router, to act as my gateway. With the added bonus of having a full server and not having to deal with the ISP for my web pages.
