erm... You will need to connect your xbox to your pc...
Then get Xbox connect...
http://www.xbconnect.com/
It depends on your internet connection...
How much experience have you in LANs and internet connections?
You need to have a a pc connected to the internet with a LAN port... The Xbox can be connected by a Cross over lan cable... any PC shop will sell you one... But it MUST be a cross over cable... theres a diff between lan cables and lan cross over cables.... Then pug the xbox to the PC... if your on XP it should straight recongnise the connection...
hang on....
Xbox does a walkthough
http://www.xboxemea.com/playtogether/xboxlivemanual/
You want to select your IPS
Then you want to go WIRED
then a HOME NETWORK
then INTERNET SHARED CONNECTION
thats what your aiming to create... once it looke like that download xbox connect and install and find a room...
Hope that helps....