You may not get a great deal of help with this problem. You see, while we are able to help with backups of dvds that you own, or downloads that you have bought from legitimate sites on the net, like Cinemanow or Movielink, movies found on the torrents are generally not legal. It is possible that you have found 20 movies on torrents that are not copyright protected, but very unlikely.
We probably can’t help unless we know more about the files that you have. You cannot tell us a great deal about the files without revealing that they are illegally obtained, and thus have this thread shut down immediately. Something of a Catch-22, yes?
Corrupted downloads as a general rule are not easily fixable. If the movies play on the computer without issues, you might have a chance. Are these avi files, or actual dvd-video?