from what I've heard from others, it's the same as the movie player and they added the ability to play roms as well. I have my supercard but still haven't gotten a CF card and reader (yet).
The movie play times, as listed on the back of the Supercard box:
128MB CF : high quality (12 minutes), standard quality (60 minutes), high compression (120 minutes)
256MB CF : high quality (25 minutes), standard quality (120 minutes), high compression (240 minutes)
512MB CF : high quality (50 minutes), standard quality (240 minutes), high compression (480 minutes)
And I've heard that high compression results in very poor quality
