You can run Windows applications on a Mac through Bootcamp. You’ll need a copy of 32bit Windows XP or Vista. http://www.apple.com/macosx/features/bootcamp.html
If you’d rather not go through this, or don’t have an extra copy of Windows handy, you can break encryption on dvds using MactheRipper or Handbrake. Handbrake only works on simple CSS protection and will convert to mp4 I believe.
MactheRipper free version is here: http://www.mactheripper.org/
It is very old however. To get the latest version you’ll have to join their forum and “donate”.