Macsome Audiobook Converter for Win converts any audio books that could be played on iTunes. The conversion is 5X speed fast, and could be the CD Quality. Moreover, it's also an .aa converter, audio book to MP3 converter.
For audiobooks in Mac OS X there is a special format M4B, which is the standard for the iTunes Store. Therefore, to be able to fill to their iPod or iPhone audiobook, not bought in the iTunes Store, you need to have the tools to create m4b files with their own hands.