Usage Rights
You can download two kinds of content from Video Marketplace: Purchase and rental. What is now called purchase is pretty much what you're already used to. You download the video and you can view it on your console with any profile. In addition, you can download and view any video on another console as long as you're signed in to Xbox Live®with the profile you originally downloaded it with. Most of the time you'll see a "does not expire" tag when you check the info for this kind of video.
Rentals are a new concept for Video Marketplace, so I want to be very clear about how this works. Think of it as a combo rental/pay-per-view deal. When you rent a video, you have 14 days to watch it. Once you start watching it, you have 24 hours to finish watching it, so long as it's still within those 14 days.
When you look at the info for a rental video, you'll see that it's tagged with an expiration countdown clock. When you first confirm the video download, the 14 day countdown will start. This countdown starts the moment you confirm your rental, whether you start the download or not. Once you start watching the video, it switches over to the 24-hour countdown clock. You can watch the video as often as you like until it expires.
One note about rentals: You have to watch them on the console you originally downloaded them on. You can't watch it on another console through your profile like you can with purchases. Also, if you delete a rental before the 14 days are up, you'll have to rent it again.