I'd recommend purchasing AnyDVD to decrypt and CloneDVD to re-author the movie and copy the VOB files to your hard drive. Yes, there are many free solutions out there, but both of these products are very well supported by Slysoft, are very easy to use, work with every DVD you'll run across, and are sometimes updated several times a week. I've used the free alternatives, but my time was well worth the investment I made in the commercial software. It's super easy to use and very reliable.
If you want to convert your MPEG2 DVDs from VOB files to some other format, Clone DVD Mobile is a great product as well. You can purchase all three in a bundle. Having said that, there are free equivalents that are about as easy to use as Clone DVD Mobile, so you may not need to purchase this one.
To try a demo version of each, download them from slysoft.com.