AppleTV doesn't just stream, it has a hard drive that can be synced to one computer, so that just about any rich media you have stored on your computer and in an iTunes play list can be downloaded wirelessly to the AppleTV device. In addition, AppleTV also can stream from up to six computers, so anything in the proper format and in an appropriate playlist can be viewed on the AppleTV from them as well.
The AppleTV will display photos from iPhoto, play music, let you watch or listen to podcasts, watch your downloaded TV shows and movies (if you bought them, they'll have to be from iTunes), let you show your own movies, and even preview songs, or download movie trailers from Apple's website directly on the AppleTV device.
For an excellent discussion and review of AppleTV, you should check out
Walt Mossberg's column. It's pretty comprehensive.
Eric
QUOTE(The Right Rev Chumley @ Mar 20 2007, 09:47 AM)

As far as I know Apple TV is just a set top box that allows you to wirelessly stream your computer (in this case anything available on itunes) to your television. So as long as you're willing to pay for the episodes it has Heroes and BSG and such. (anything you can download or buy from iTunes)
anyone have any really good knowledge of what this puppy can do?