I found this on google:
You will need a network card in your PC, and i'd be very very very suprised if a 2 year old machine didn't have one. You'll need this card to connect your 360 to your PC using a process called 'internet connection sharing'(ICS), unless you get a router, but even then you will still need a network port for the router to connect to your PC, unless! you go the wireless route, then you will need the wireless adaptor for the 360 and either a wired or wireless newtowrk card in your pc
Michael - depends on what each machine is doing. eg on the current xbox you can easily play games and surf the internet, use msn etc with no problems. Things get a bit funky if you are downloading music or whatever on the pc whilst trying to play games, so if you can avoid it don't do it
I dont know about the 360 but can offer a little advice re the current xbox live.
You will probably have a network connection on your pc, I have. At the moment, i have a ethernet cable running from my computer to my xbox. You then change the properties of your internet connection on your pc to enable iternet connection sharing. The xbox should then detect the setting from the computer when they are both switched on. This works fine for me.
With regard to using both at the same time. It should only affect live play if you are downloading on your pc using the same internet connection. This might cause some lag in the game.
Hope this helps. I'm certainly no expert but, as i say, this works for me. Im on 2mbps Tiscali.
Look around, you will find people who are doing it. I have never had a XBOX so helping you is a bit hard.