I’m a huge fan of audiobooks, especially listening to them on my iPhone through bluetooth while driving.  Here’s the process I use to load them into iTunes so my iPhone treats them as audiobook files and not music:

1. Open iTunes on your computer
2. Insert the first CD of the audiobook
3. Select the CD in iTunes
4. Select all the CD tracks for that disc and select “Join CD Tracks” from the “Options” menu
5. Confirm that the import settings are set to “AAC Encoder” and “Spoken Podcast” (32kbps mono/64kbps stereo)
6. Click the “Import CD” button
7. Repeat steps 2-6 for all the CD’s for the audiobook
8. Select all the tracks of the audiobook, right-click and select “Get Info”
9. Click “Yes” when iTunes asks if you’re sure
10. Change the Artist to the audiobook’s author
11. Change the Album to the name of the audiobook (book’s title)
12. Do a Google Image Search for “[Title of book] audiobook” to find a picture to paste in the Artwork field for the book
13. Click the “OK” button
14. Update the individual track information fields (e.g. “BOOK TITLE, Disc 1”, etc.)
15. Right-click on one of the files in iTunes and select “Show in Windows Explorer”
16. Change the suffix for each file from “m4a” to “m4b” so iTunes will treat the file as an audiobook
17. Drag the files back into iTunes so they will be added as a book
18. Delete the old files from iTunes (which will no longer work since you’re renamed the filenames)
19. Sync your iPhone or iPad to have a mobile copy of this audiobook