Instructions
Official Xbox 360 Wireless G Adapter
Purchase the official Xbox 360 wireless G adapter, which is available through the Xbox website and online and local gaming stores.
Insert the USB plug into the USB port located on the back of the Xbox console.
Use the Xbox 360 on-screen menu to select and connect your wireless network to your console.
Using a Computer with Wired Internet Access
Connect an Ethernet cable from the computer to the Xbox console.
Enable the wired LAN port on the computer.
Select the Wireless Connection icon and select Properties, then Advanced Tab. Select a box marked "Allow other network users to connect through this computer's Internet Connection."
Select the Wired LAN Connection, which will probably be marked as "Local Area Connection." Click OK.
Test the Xbox 360 Internet connection using the console's on-screen menu under the Network Settings options.