How do I set up my Xbox 360 to the internet?

I have had the 360 for over a year now and it is still not hooked up to the internet. I just got Halo 3, and I want to get online. Here’s the catch…

1. I have a three story townhome. It is pre-wired for networking and has Cat-5 jacks in every room, including right next to the Xbox, which is on the middle floor. The home-run panel is on the bottom floor.

2. I have Comcast high speed internet, meaning it comes in to the house in the cables lines. My computer is on the top floor, connected to the cable modem and wireless router.

3. I bought the wireless antenna for the Xbox, but after several vain attempts to connect to the internet wirelessly, including several with the assistance of the MS Xbox support team, I have given up on this. My wireless router is not supported.

4. I want to hook up the Xbox to the cat-5 jack next to it.

QUESTIONS:
1. Do I need to add a router in the home run panel on the bottom level to direct the traffic from the Xbox on the middle level to the cable modem on the top level?

2. Or should I be able to do this all without having to add a router?

3. Can I use the wireless router upstairs (without moving it downstairs) to link the jacks?

4. If I need a router downstairs, what kind should I get and how do I hook it up?

5. Am I complete tard for asking this many questions?

Recap…

Top Level:
Cable Modem (Comcast)
Belkin Wireless Pre-N Router
Computer

Middle Level:
Xbox 360

Lower Level:
Network home run panel

Help!