I think this is what you have to do:
Get a wireless penstick for your computer.
Currys - Shop for Wireless Network Cards - Belkin F5D7050UK Wireless 54G USB Networking Adapter=
Then get yourself a wirelesss router.
Currys - Shop for Wireless Routers - Belkin G+MIMO Modem Router & Notebook Wireless Networking Bundle
Then you need to check with your ISP that that is ok.
Your son might need to reconfigure his xbox.