Audible .aa files to mp3.

If you have need of converting an Audible .aa (that's file format 4) into an mp3 or similar (because you can't find anywhere that sells the thing DRM free):
i)  You'll find plenty of shareware apps that claim to be able to do it (like SoundTaxi and TuneConvert) and (a) it looks like they can if you want to pay the price (or they'll only do 90 seconds), and (b) they all look like they're by the same people / based on the same stuff.
ii)  Alternatively, if you're more cheapskate (in my case I only wanted to convert a single file) then there's a post from 2007 that (if you persevere with getting the Visual C++ DLL installed on Windows 7 64 bit) still seems to more or less work:   http://forums.afterdawn.com/thread_view.cfm/589613

I didn't want to install iTunes and try to burn to CD then re-rip.   [I dislike iTunes, though frankly that route would have been less system-invasive than the stuff I ended up doing.]