The article is correct as to space requirements to rip double-layer commercial DVDs. But don't be fooled that you need to buy any programs, the freeware alternatives are superior, having been designed by video hobbyists. There's good basic information on this site:
http://www.mrbass.org/
You're probably aware that many DVDs carry newer protections designed to make it more difficult to back up one's movies. Such as ARccOS, Ripguard, et. al. There are a number of ways to deal with them, but the easiest I've seen is RipIt4Me. It's a clever program, integrating DVDDecrypter, DVDShrink, and FixVTS. So far it handles anything out there. If the protections are improved, the program likely will be as well, as the author has updated it often, so far for bugfixes mainly. Get it here:
http://www.ripit4me.org/
Here's another site, it should have the answers to just about any questions you may have:
http://www.videohelp.com/dvdbackup
Good luck.
