IIRC, Lite will fit onto a stock Xbox HD if you blow away everything else on it. I believe the previews are just screenshots and not movies, and it's a limited selection of games (though still hundreds).
Full requires a larger HD, has animations, and more games.
I gave up on keeping up with it, to be honest. The guy behind it is quirky and seems to be continuously updating it. I'm not convinced that he's actually improved/changed the emulation any, but the Visionary menus are kind of cute.
It's a fun way to dust off an Xbox, but I think you're better off going with a PC for anything serious.