How do I authorize my Audible Account?

From http://audible.custhelp.com/app/answers/detail/a_id/3131 :

Section 5 -- Authorizing your Audible Account in iTunes

Summary:

You can use your Audible purchases on up to 4 different computers and 3 Apple devices at one time. When you can play or sync an item you've purchased, your computer and/or device is authorized for that Audible account. If you have multiple accounts you must authorize for each account. Authorizing your computer in iTunes will authorize your Apple device when you sync it with iTunes.

To authorize a computer/Apple device to play purchases from your Audible account:

1. 1. In iTunes, locate an Audible title from the Books or Audiobooks section under Library. If your Audible title(s) are not listed in iTunes click here for instructions on importing your Audible titles in to iTunes.
2. 2. Select the Play button or double click on the title. If the computer is already authorized the title will play. If the computer has not yet been authorized, iTunes asks you to enter in your Audible username and password.
3. 3. Simply enter in your Audible username and password you've used to purchase the Audible title and select OK. If you are unsure of which account the title was purchase on, right-click on the title and select Get Info. Under the Summary tab there will be an Owner field. The Owner field will show you the account you've used to purchase that title.
   Note: You must be connected to the Internet during the authorization process.

Common iTunes Authorization Errors:

• Receiving a Invalid Username or Password error? Click here in order to reset your password and/or retrieve your username.
• Not seeing any Audible titles in iTunes? Click here for instructions on importing your already downloaded titles to iTunes.
• Receiving an error message during authorization? Click here for a list of common error messages.
• Receiving an error regarding reaching the limit of activations? Contact us in order to reset the activations on the account.