If you use Google (a popular search engine) and search for DVD ripper, there are tons of free apps that will rip dvd's to files and enable you to pull the audio as a seperate stream.
Its not a process meaningful to these forums but there are DVD forums that can guide you.
Here's a link to get you started, probably the best I have found for newbie DVD rippers:
http://dapcentral.org/faqs/vcd/
Good luck, maybe you can post some of the results of your work for us all to share.