4th generation and later iPods (including the iPhone, excluding the Shuffle) are able to play back audiobooks at a 25% slower speed without changing the pitch. I started looking for some way to convert my existing .mp3 files into audiobook format, found this little shareware Windows utility that does exactly that:
MP3 to iPod Audiobook Converter
http://www.freeipodsoftware.com/
After you convert your file to the .m4b format, you’ll need to copy it over to your iPod using iTunes by first importing it to your music library, then copy it from your library to the iPod.
On the iPod, find the options menu, where you should be able to set the playback speed to slow/normal/fast. The slowed down quality isn’t pristine, but good enough for learning tunes.