I've been doing this for years on the PC side to rip AudioCommentaries from The Simpsons dvd's. (If you're a fan then they easily are the best out there and actually work well on the go).
On the mac I was recommended iCommentary but cant get it to work. I'm a mac newbie so I dont know what I'm doing wrong, but if anyone else gets it to work then give me some tips. Its supposed to be perfect for extracting just the audio track.http://icommentary.kempa.com/