I know there aren't a lot of Mac users around, and I'm sure there are a number of people who won't be willing to pay $14.95, just for this, BUT....

The June 2004 issue of MacAddict magazine has over 500MB of AAC audiobook files (although not of really high quality), licensed to them for their cover disc from www.audiobooksforfree.com, consisting of:

Hound of the Baskervilles
His Last Bow
The Return
The Sign of Four
A Study in Scarlet
The Valley of Fear
Memoirs of Sherlock Holmes
Case Book of Sherlock Holmes
The Adventures of Sherlock Holmes

44 or so hours in all of audio, on one CD. The disc is easily readable on any system. I'm using WinAmp 5 to play them on a PC, though you could also use iTunes (on Windows 2000 and XP) or RealPlayer 10. For Linux/UNIX geeks, I'm honestly not sure what players have AAC support....