The legalities surrounding dvd back-up has been a topic of fierce debate for quite some time.
In Australia here you are legally allowed to keep a back-up of your original copy-righted dvd and cds but rules apply.
I'm sure the "rules" can change depending on where in the world you are.
The easiest way is to use dedicated software to perform the task for you.
DVDfab / DVDfab platinum is excellent dvd back-up software. Two clicks of a mouse and you're done, it's that easy.
It is Vista compatible and free for 30 days, you might even be able to get all your DVD's backed up.
Here's a link:
http://www.softpedia.com/get/CD-DVD...
P.S. I have found that DVD-R is the best blank media to use.