- Have you imported the audiobooks into your iTunes library? (Yes, I know that may be an obvious thing - but I simply want to make sure.)
- If you have them in your library and you have perfomed a Sync, have you tried using the Search facility on your iPod to see if they are on it, but simply not where you expect them to be? (I don't have any audiobooks, but Podcasts and movies sometimes end up in a different section to the one I expect.)
If you find it, but not where you expect it to be, condier the following. To be an Audiobook, the file must be listed as Audiobook in iTunes. So it's not enough for it to be downloaded as an audiobook. Once you find the file in iTunes, look at File/Get Info/Options>Media Kind. If the Media Kind is not Audiobook, thta's why it's not in Audiobooks on the iPod. Change the Media Kind in iTunes and then Sync the iPod to iTunes. That should sort it out.