I'm going to let this one speek for itself:

When Apple opened the iTunes Music Store, they licensed a technology called "FairPlay" from a company called "Veridisc". FairPlay is a Digital Rights Management (DRM) system that limits a users rights on a digital media file that they've purchased and presumably downloaded. In the case of Apple's iTunes Music Store, when a user downloads an audio track from iTMS, it is a "Protected AAC Audio File". When used as intended, these files can only be played through the iTunes program itself. Furthermore, a particular computer must first be "authorized" to play the given file. FairPlay allows up to three computers and unlimited Apple iPods to be authorized to play the file. As DRM schemes go, FairPlay is only moderately offensive.

So what will playfair do for you? The playfair program is quite simple. It takes one of the iTMS Protected AAC Audio Files, decodes it using a key obtained from your iPod or Microsoft Windows system and then writes the new, decoded version to disk as a regular AAC Audio File. It then optionally copies the metadata tags that describe the song, including the cover art, to the new file.

I just got my first taste of iTunes DRM the other day when I coppied some songs I bought from one of my laptops, to my desktop imac, and then onto my other laptop and started getting some static. I'm planning of retiring my 15" G4 TiBook sometime this year and I know that the new machine I get is only going to complicate this more. MacNN points out that this app requires Xcode and runs from the Terminal.