When i first got my 360 i was connecting through my laptop, but since i don't use xp anymore i cant remember off the top of my head.
Here's a random link from google. I've pasted the important part, but if you get stuck, check the link and follow the rest of the steps.
Addy:
[http://www.trap17.com/index.php/internet-connection-sharing-xbox-360-laptop_t54749.html]
"Supplies:
Laptop connected to internet
Xbox 360
Ethernet Cable (comes with Xbox, can use any other though)
1. First, have your xbox turned on. Also have your PC on, since this next part is all with the computer. This will probably work with a wired connection as well (but you could probably just hook straight up to your router or modem then), but here it is. First go to start and go into your control panel. Switch to classic view by using the link in the top left corner of the window. Find Network Connections and open it.
2. You should see a "Local Area Connection" (unconnected, this is for the connection to the Xbox) and your internet connection (mine is called "Wireless Network Connection"). Connect the ethernet cable to your laptop and to the back of the 360. Enable the "Local Area Connection". After it is completely connected, disable your internet connection, in my case "Wireless Network Connection". Once is it disable, right click the internet connection and click properties. Go to the Advanced tab and check off "Allow other network users to connect through this computer's internet connection." Allow this to finish, it may take a little bit. Once it is done, your internet connection should say shared next to the status of the connection.
3. Enable your internet connection. Once it is fully connected, right click the "Local Area Connection" and click repair. Allow that to finish. On your Xbox, find the system panel and navigate through it until you find "Test Connection to Xbox Live". Test the connection. If it works, congratulations, you don't need this next part. For some, at this point, they get a DNS error. There are a number of ways to fix this. None of them worked for me however (at least on the places I looked). So I found my own way. If my way doesn't work for you, then you can search in google for it and you should get a number of other troubleshooting tips."
