Apple has released a firmware update for the AirPort Extreme Base Station with 802.11n.
The AirPort Extreme Base Station with 802.11n* and Firmware 7.2.1 is Wi-Fi certified for 802.11n* draft 2.0. This update also includes bug fixes and security updates.
This update requires AirPort Utility 5.1 or later. If you have AirPort Utility 5.0 installed, you can update to AirPort Utility 5.2.1 by installing AirPort Base Station Update 2007-002:
The 4.6MB download is available for download or through the AirPort utility application in Mac OS X.