Over at eHow they've got a pretty easy to follow tutorial that'll show you how to rip a DVD to your Windows PC's hard-drive.
It's kind of a shady process, involving a mysterious piece of software called DVDDecrypter, but it could come in handy. Say, for example, you're wanting to bring a hard-drive full of movies to watch while on vacation.
If you decide to do this, heed the warnings and remember that if you're ripping a DVD for the wrong reasons, you might be in for some trouble. It's quazi-legal, so proceed with caution.
Update: several readers have written in to say ripping commercial DVDs for your own use might be totally illegal. Erica points out this nice summary of the legal implications involved.
How to Rip DVDs [eHow]