Yeah, you need some kind of router. Assuming that your buddy was only provided one IP address (which is probably dynamic anyway), you're going to need a router that can act as a DHCP server to provide you with additional NAT'd IP addresses.
You're other option would be to run the cable through his computer and set up Internet Connection Sharing, this sucks though because his computer will always need to be turned on because it's acting as a proxy server.
I'd recommend the first one. Better yet, get a wireless router and install a wireless NIC in your computer, that way you won't even have to run wires into your room..............how cool is that?