Copying DVD movies could be illegal. In fact what you want to do is probably illegal... unless you own the movie. So just in case you do...
There are specialized forums that deal with DVD authoring, copying, etc. You might want to visit AfterDawn, Digital Digest, and many more. Just google DVD copying and you'll get a ton of hits. Most likely, they'll be hits to places like I mentioned above.
The thing about copying DVDs is that some can be done directly, and some can't. Most "released" movies are protected by some kind of macrovision code. There are many programs that can strip the macrovision encoding from the movie during "ripping". Ripping is basically taking the files off the DVD and placing them on your computer for processing. Once on your computer, and in the case of released movies, the file size will most likely be too large to fit on a standard 4.7gb DVD. This is when you will need to process the files and "shrink" them to fit on a standard DVD. Or, if you can spend a little more money, and your DVD writer is capable of burning Dual Sided, you can purchase Dual Sided DVDs and burn them directly. If not, then you need to shrink the files.
A good ripper (one of the old time best) is DVD Decrypter. It's no longer being developed, but with enough hunting you'll still be able to find it. There are many other rippers, and you'll just have to read the forums for advice on the latest and greatest. Once ripped, a good shrinker is... DVDShrink. Very easy to use, and does an excellent job of processing the files.
After you process the files, you can burn them using programs like Nero (the best as far as I'm concerned). Nero is not free however so be prepared to spend some money.
Of course, if it's a released movie, then you have to remember that copywrite laws apply... so anything you do, you take responsibility on your own. (that was my disclaimer!)
Start Google-ing!
