The Xbox 360 apparently will not recognize any network with security, whether WEP or WPA and Microsoft's tech support apparently is telling customers that Apple routers are not recommended. So would you be willing to entirely disable security on your wireless network to connect to your Xbox? That's apparently one way of making the connection work. Some readers report that turning off security and closing their network (not advertising the SSID) and using MAC address filtering work. You can join the Xbox/Airport Extreme discussion here.