DVD Decrypter will rip the CSS from the disk so you can burn the resulting files to a blank. It can also be used to compress the video since most consumer DVDs are ~9G (dual layer), and most blank DVD-R/+R disks are only 4.5G (single layer).
They were sent a cease and desist a year or two ago, so I don't think ti's being actively developed, but I'm sure there are old copies floating around.
Keep in mind that using the software violates the (lame) DMCA act and technically makes you a criminal. Yes, even if you're only using it to backup something you already own. That's why it's lame.
Doom9.com is the definitive site with tons of info as well. They might list a better program:
http://www.doom9.org/