Ok, I use this for my Xbox and it works, Its cheaper that buying a Wireless adapter.
What you need:- A PC/Laptop with wireless LAN Network Plug (Not in use)
- Networking Cable
What to do:Step 1: Open up your network management centre.
Step 2: Get your Wireless and LAN Port and Highlight them both (Hold Ctrl).
Step 3: Right Click on the highlighted items and Select 'Bridge Connections'
Step 4: Plug the Network Cable into the port and into the Xbox, and there you go, And Xbox live connection.
Its better if you have a laptop, Its more mobile, but Desktops are okay (Thats what I use).
(I will add images later)