I don't think there is much you can do , It's a bit like mp3 compression , U lose some elements the more you compress but when expranding they are gone so u cant have them back. I have tried editing stuff recorded from my tv card but every step in the process seems to make the video poorer. My card only supports avi and mpeg modes so I havent tried working with any other file types.
Most movies found online would be Illegal rips anyway and you would be much better off going out to see the film in a cinema, or hire the video.
I have tried some of the "trial" software to see how good they back up and i was greatly disappointed at the quality. If you feel like trying to back your own up, try here: www.cdrbase.com
they have some excellent tutorials on making high quality back-ups. I have had nothing but GREAT results with near the original quality.