there are a number of ways of doing this.  See http://www.videohelp.com/virtualdubaudio.htm for a way.

 

Personally, what I do is rip the dvd with DVD Decrypter, the switch to DVD Lab to extract the separate video and audio streams, then use either headac3he or Media Studio Pro to convert the ac3 to a wav.  Then Cool Edit to edit if necessary.  CDRwav to cut the tracks. But not all of these are free.  The above linked guide is for a free program which will do it for you.

 

-paul