So many options, you can jsut take the audio out of your DVD player, computer or whatever and plug it into the input of your recording device (o input on the computer).
Something like audacity ought to do the trick if you want to record to PC, and you can probabaly consult help fules there to monitor the DVD's audio signal and record it seperately as well.
Programs like DVD shrink can decode the DVD and let you get at the audio files as well.
Daav