DVD's are in a file format VOB, what you need is some software to convert VOB files to MP3 files - have a look on google for "VOB to mp3" and see which software you feel is the best for you to use to convert these - theres loads of sites advising how to do this, but some are charging for the downloads.
I managed to do it by playing with the recording input settings on my sound card so that I could record from the 'mixer' rather than line-in or mic. I used musicmatch jukebox to do the recording (to either wav or mp3).