Audible content can be played on PCs or Macs. The comments below regarding iTunes apply to both platforms for the most part, and differences are pointed out where applicable.

1. Audible Basics
2. Audible File Formats
3. iPod Software for Audible
4. Importing Audible Files
5. Transferring Audible Files
6. Bookmarking-Pause/Stop-Resume
7. Audible File Navigation
8. Browse the forums for more info...

1. What is Audible?
Audible.com offers a wide selection of digital spoken word audio content. Audible files can be downloaded and played on computers and transferred to portable devices such as the iPod. Audible's library includes audiobooks, archives of NPR & PRI radio shows, speeches, lectures, interviews, comedy, drama & poetry, and just about any form of spoken word content.

Audible content can be purchased from Audible.com or through the iTunes Music Store. For occasional listeners, titles can be purchased individually, and for frequent listeners, a variety of money saving subscription plans are available at the Audible website.

2. Audible File Formats

A. Enhanced playback features
B. Audible vs regular MP3
C. Audible file formats

A. Enhanced playback features
Audible utilizes a proprietary file format that includes custom features that improve the user experience over regular MP3 formats when listening to spoken word audio.

Audible files provide the ability to bookmark your playback position on each and every file stored on the iPod. You can switch between Audible files, exit and listen to music, and go back and forth and the iPod will remember your last position played and pick up where you left off. Audible files will also maintain your bookmarks when you snyc your iPod with iTunes and / or transfer additional files to your iPod.

Also, Audible files are broken up into different sections, either by timed intervals, chapters, or program segments. These segment markers allow you to quickly advance backward or forward to the next section.

With Audible's compression technology and advanced file navigation features, entire books can be stored in a single file. The entire 62 hour volume of War and Peace, for example is contained in only three Audible files.

iPod Audiobooks Menu and Variable Speed
4G and newer iPods as well as iPod Mini with current firmware provides and audiobooks menu option on the main menu to seperate books from music. A variable speed control is also available for audiobooks. Files recognized as Audiobooks will be ignored when listening to Music files in shuffle mode.

NOTE: In order for the iPod to recognize a file as an Audiobook, it MUST BE in either Audible file type (.aa) or Apple's .m4b format. It does not matter what is in the genre field says. The file format is the identifier.

B. Audible vs MP3
In contrast, if you rip audiobooks from audio CDs, every chapter or couple chapters will be contained in a separate file. So with a 6 hour abridged audiobook from CD, you are likely to end up with 30-40 separate files. The iPod will NOT remember your last played position on MP3 files.

Books ripped from CD's in MP3 format cannot be bookmarked. For more info on bookmarks, see section below.

C. Audible File Formats
Downloads from Audible.com website are available in four different formats. ONLY formats 2-4 will play on the iPod. The different formats represent different audio quality and files sizes, with four being the highest quality/largest file size.
I recommend Format 4 on the iPod for highest sound quality since space is not really an issue on the iPod. Audible's Format 4 is similar to an MP3 files at 32kps. (Format 3 offers a good compromise for dial-up or where disc space is minimal).

Audible files purchased from the iTunes music store are encoded in Apple's AAC format, and provide the same enhanced playback improvements as files with .aa extension downloaded directly from Audible.com.

3. Software for using Audible on iPod
IMPORTANT UPDATE REGARDING iTUNES 4.5 or higher for WINDOWS-5/04
Audible now offers the Audible Download Manager for iTunes version 4.5 and higher. This applet streamlines the downloading and file management process. For most users, you will only need to install the iTunes Plug-In. You do not need to install AudibleManager unless you will use Audible on non-iPod devices or use AudibleManager's automatic subscription downloading feature.

NOTE: If you run the full version of AudibleManager software in addition to the Download Manager for iTunes, set the Watch Folder in AM to the same location as the iTunes Download Manager. That way, files downloaded with the iTunes Download Manager will also appear in your AudibleManager library.

The Audible Download Manager is available at audible.com/software

More information on using iTunes 4.5 is available here.
http://www.ipodlounge.com/forums/showthread.php?s=&threadid=30939

ITunes (Mac or PC)

iTunes is used to manage and transfer files to the iPod. Once you install iTunes, AudibleManager (on PC) will only be used as a download manager for downloading Audible files. After downloading, you must import the Audible files into iTunes. (Click Add Folder in the iTunes file menu and select your Audible file folder).

Switching to iTunes (4.5 or higher) from AudibleManager
If you switch to iTunes for Windows, you will no longer need or be able to use AudibleManager to transfer to your iPod. You must use iTunes.

HOT TIP: If you have AudibleManager installed, after you install iTunes, change your device setting in AudibleManager to "NO DEVICE" This will prevent AudibleManager from trying to connect to your iPod each time you connect. The application will also launch faster and requires less system resources.

Apple has a knowledgebase article on using Audible files on your iPod.
http://docs.info.apple.com/article.html?artnum=61695

For more details on switching to iTunes from MMJB/AudibleManager:
http://www.audible.com/iPod/FAQ.html

Notes regarding other applications.
Some third party applications also provide Audible support. However, be aware, you may run into conflicts when using multiple software applications or those other than recommended by Apple and Audible.

4. Importing Audible Files in iTunes
With Audible's Download Manager for iTunes, files downloaded from Audible.com are automatically imported into iTunes and will appear in a playlist titled Audible.

Files downloaded from iTunes Music Store:
If you purchase Audible books through iTunes Music Store, your downloaded files will automatically download into your iTunes library, ready to transfer to your iPod.

5. Transferring Audible Files

Audible Files are transferred to the iPod just like MP3 or AAC music files. You can transfer files individually or create Audible playlists. Audible files can be transferred manually, or with the synch function. In either case, follow the method for transferring MP3 files to your iPod.

Help using iPod
The iPod support page from Apple is a good place to start if you are completely new to the iPod.

http://www.apple.com/support/ipod/

For complete details on using iTunes, including adding files, and transferring to iPod, Apple provides some nice tutorials at these links:

Help using iTunes:
Windows
http://www.info.apple.com/usen/itunes/windows/
Mac
http://www.info.apple.com/usen/itunes/

Help using Media Center 9.0 (MC9)
http://www.musicex.com/mediacenter/help/default.htm

6. Bookmarking-Pause/Stop-Resume

The iPod is designed to remember your last-played position in Audible files and resume at the point where you left off when you return to that file. The playback position is remembered in each Audible file you listen to. For example, you can listen to an audiobook, stop it, switch to another Audible file, play it for a while, stop it, listen to some MP3 or AAC music files, come back a week later, and the iPod will still remember where you left off in the each of your Audible files.

The last played position is also retained when you transfer additional files to or snych your iPod with iTunes.

Note on Bookmarking: The iPod does not allow the multiple, manually selected bookmarks like the Audible Otis player does. The iPod only bookmarks the playback position when a file is paused or stopped.

IMPORTANT: For Gen1 and Gen2 iPods, you must update your firmware to version 1.3 for the bookmarking feature to work.

UPDATE: Instructions on creating bookmarkable AAC files can be found here:
http://www.ipodlounge.com/forums/showthread.php?s=&threadid=25502

7. Audible File Navigation

RW-FF buttons: holding the RW or FF buttons advances the file forward or backward in five-second increments. Note that you must HOLD the button down, not just tap it.

WARNING: A single touch or the RW button will return you to the beginning of the file. When rewinding, be sure to hold the RW button until you hear the track rewinding. Better yet, I recommend using the "scrubbing" method described below to avoid accidentally touching the RW button and sending you back to the beginning of the book. Also, use the hold button during playback t avoid accidental button activation"

Rapid Advance (aka "scrubbing")
To rapidly advance to any point in your Audible file, touch the center button once. The volume bar will turn into a file navigation bar. Use the scrollwheel to rapidly advance backward of forward to any point in the file.

Section Navigation
Many Audible files are broken up into segments. The segments may be chapters, timed intervals, radio show segments, etc.
To use the section navigation feature, tap the center button once. Section indicators (when available) are indicated by vertical bars in the file navigation bar. Use the RW or FF buttons while in file navigation mode to jump from one section to the next.

NOTICE: The section navigation feature is available only on 3G iPods. 1G and 2G models operate the same as 3G with regard to FF/RW and Rapid Advance (scrubbing), but you will not see the segment markers in the navigation bar.

8. Browse or search the Audible For iPod Forum for more info.

http://www.ipodlounge.com/forums/forumdisplay.php?s=&forumid=46