Playlist Magazine has a nice little tutorial
for converting audiobooks you obtain from somewhere other than Audible.com or the iTS into iTunes recognized Audiobooks. For instance if you rip an audiobook CD, or download free audiobooks from any of a number of sites
, you can convert them so that they will appear as Audiobooks on your iPod and in iTunes which gives you access to bookmarking and speed controls.
Basically, it consists of joining the tracks and converting the result to a special type of AAC (.m4b), but check out the tutorial
for full details.