I've got an Airport Extreme and an external USB Hard Drive formatted with NTFS. (And a LAN of Windows XP Machines.)
The drive works perfectly when connected directly to a PC.
When it's connected to the AE, however, the Airport Utility sees the drive and lists it in the Disks list, but the drive doesn't appear on the network (as near as I can tell.)
Can the AE handle NTFS formatted disks? The documentation is vague on that point.