Yes. It's a good way to not have to spend the $100 on the 360 wireless network adapter, although if you have the cash it's a great product.
Have him plug the 360 into the laptop's ethernet port.
Assuming he's in XP:
- Start
- Control Panel
- Network Connections
- Right click his wireless connection
- Click Properties
- Go to the Advanced Tab
- Check the "Allow other network users to connect through this computer's internet connection" box
Hit OK, and it should work.