Instructions
Turn off the Xbox 360.
Latch the wireless adapter above the console's rear USB port by snapping its two flaps into the two holes located to the sides of the identification sticker.
Plug the wireless adapter's power wire into the USB port, located just below where the wireless adapter mounted to the console.
Extend the antennae upward to give the adapter better signal range.
Log into Xbox Live. Notice the log-in attempt fails and that the console prompts you to test the connection.
Highlight and open "Yes, test connection." This opens an Xbox Live configuration screen.
Scroll to the first option, "Configure Network," and press A.
Push A again on "Wireless Mode." This is the first option on the resulting page.
Locate wireless networks by highlighting "Scan for networks" and pressing A. The console will take a few seconds to search for wireless networks. Afterward, the Xbox 360 will display available networks.
Highlight the network you wish to connect to then push A. One of two things may occur: you'll either be connected to the Internet or your console will ask you for the security password.
Input the password into the correct field then press the Start button. This connects you to the network and finishes the adapter installation.