Most commercial DVD discs have built-in copy-protection which prevents copying for obvious reasons. The fact that you only want to copy from them for your own use makes no difference to the copyright holders. Long gone are the days when they turned a blind eye to copying for personal backup reasons. It's not legal any more, and just to make sure you comply they use copy-protection.
Under UK law there has never been any provision to make copies of copyrighted stuff for your own personal use (aka "fair use" in other countries). You cannot convert a CD to a tape or MP3 legally and play it in the car and claim it as fair use, for example. Likewise it is illegal to rip music to the computer without consent of the copyright holder. Under the same principle (but clarified in a court of law) it is only legal to record TV programmes providing you only record for you and you destroy the recording after 7 days. In reality it's completely unenforceable and mix-tapes (as they used to be called) were going on long before the ability to share them across the world was even thought of.
The situation is more clear-cut in other territories, namely America, for example, where it is permissible to rip and copy things under fair use(and has been enshrined in court cases over there).
The copy protection has been there since the concept of licensing (key word) copies of commercial to people at home. You'll find it on commercial videos, DVDs and the odd music CD, considering Sony managed to completely screw it up in 2005: http://en.wikipedia....tection_scandal
That being said, whether what the original poster wants to do would class as fair use depending on which part of the world they're from.