Of course the first thing I did with my Airport Extreme base station (7.2.1) was to try to share a USB hard drive over it. What I found was that the shared disk drive would not automount on my new Leopard MacOSX system. Fortunately after much searching I found my answer on the Apple Forums. You basically had to remove the Airport utilities and reinstall them from the Airport Extreme Installation CDROM.

1. In System preference > Acounts > Login Items, remove Airport Base Station Agent
2. Reboot
3. On the hard disk Macintosh HD > System > Library > CoreServices delete the Airport Base Station Agent and Apple80211Agent
4. Reinstall the Airport Extreme software from the Install CDROM
5. In System preference > Acounts > Login Items, add Airport Base Station Agent from its location in the hard disk Macintosh HD > System > Library > CoreServices folder
   

After the next reboot the USB drive should auto-mount again.

Tags: Airport Disk