We happen to use an 802.11n AirPort Extreme as our router, so we put today's new firmware upgrade to the test to see if TIme Machine really does do networked backup to an AirPort Disk. In case you're wondering, AirPort Express never supported AirDisk, so it won't do Time Machine over the network—our testing confirmed this. With the Extreme, it requires only a base-station firmware update and a plugged-in external HDD. When we logged into AirPort Extreme using the Finder and clicked on the folder representing our AirDisk, Time Machine was able to spot it, no problem. [Time Machine on Giz]