Instructions
Open the Xbox 360 CD tray and insert the Wireless N Installation disk, then close the tray.
Turn off the Xbox 360, then turn it back on. The update utility should start automatically on reboot.
Select "Yes, update now" when asked if you wish to install the new software.
Unplug any Ethernet cables connected to the Xbox 360.
Wait until the installation is finished, then plug the Wireless N adapter into the USB port at the back of the Xbox 360.
Remove the install CD from the Xbox 360's CD drive and restart the Xbox.