iTunes 10 for Mac: Usage rights for iTunes Store purchases
Movies, TV shows, and certain other items purchased from the iTunes Store are protected by Digital Rights Management (DRM). These protected purchases can be:
Played on up to five authorized computers
Synced with your iPod, iPhone, or iPad
Synced with or streamed to your Apple TV
If you have older iTunes Store purchases that are now available as iTunes Plus downloads, you may upgrade your existing purchases. To do so, visit the iTunes Store and follow the onscreen instructions.