Apple TV Source notes that the latest 2.0.2 update makes internet radio work a little better with the Apple TV. Basically you can play internet radio streams on the Apple TV if you have it synced to an iTunes computer with a playlist containing the streams. Before the update the source computer had to be on for this to work. Now, however, the Apple TV will retain the playlist even without the iTunes computer until it is restarted (it will retain the playlists even if put to sleep). The original post has complete instructions.