Apple has posted an AppleCare Knowledge Base Document that explains how authorization works within iTunes 4 and how to authorize and deauthorize a computer. Make sure you don’t forget to deauthorize your Mac before you sell it or donate it or you might regret it.
“Authorization is a way to help protect the copyrights on the music you buy. You can listen to music you purchase from the online Music Store on up to three different computers. When you play a song you’ve purchased, your computer becomes ‘authorized’ to play music purchased using your Apple Account. Note: Songs that you encode in AAC format from another source than the Music Store do not need to be authorized.”
“To authorize a computer to play songs purchased using your Apple Account, select a song you’ve purchased (in your library or the Purchased Music playlist), and click the Play button.”
“If the computer is already authorized to play songs purchased using your account, the song plays.”
“If the computer has not yet been authorized to play songs purchased using your account, you’re asked to enter your ID and password. Enter the Apple ID and password for the account with which the song was purchased.”
“You should deauthorize your computer before you sell or give it away.”
To deauthorize a computer:
1. Open iTunes.
2. Choose Advanced > Deauthorize Computer.
3. Select “Deauthorize Computer for Apple Account” and enter your Apple ID and password.
Note: Initializing the drive will not deauthorize the computer. If you will be initializing the drive prior to selling or donating your computer, deauthorize the computer first, then initialize the drive.
The Knowledge Base Document is here.