If the DVD is not that scratched, you can try:
DVD Decrypter, open settings, click the I/O tab and select ignore read errors and set retries to 0. Then try to rip the files. The DVD will have problems where the read errors will occur but you will watch the most of the movie.
Try a products like 321Studios DVDXRescue which does the same thing actually but with an error correction mechanism.
Get it here:
http://dvd-guides.com/forum/viewtopic.php?t=5I these does not work, try what Tank suggested you and if you fail again, then you can throw away the DVD safe and easy! :?