do for free with dvd decrypter:
1) click "mode", select "ifo"
2) stream processing tab - click "enable stream processing", deselect everything except the audio track you want
3) hit the "decrypt" button
The ripping part is done, most likely you will have an ac3 file, or possibly an mp2 or wav file depending on the dvd. You can play these files as is, or convert them to mp3 or whatever using any of these free tools:
A) besweet or belight: good for converting ac3 to mp3, maybe a little complicated for beginners
B) dbPowerAmp: converts all audio into any other audio format, you may have to download extra codecs to get the desired format
C) Winamp - options - preferences - plugins - output: select "diskwriter". Play the file and it will be written to the hard drive into wav or whatever (haven't used in a while). Remember to change output back to direct sound when you are finished
D) Audacity - probably it works to accept ac3 as input, you will have to also download the "lame mp3 codec" package if you want to convert to mp3. Since this is a full fledged audio editor, you can also cut out silence and junk at the beginning and end of the audio file
The DVD audio ripping is pretty easy, converting to mp3 and such might take a little effort if you're new to these tools, but once you have it down straight you can use them over and over w/o difficulty.
One final word- DVD Decryptor may not be able to handle the latest types of encryption used in movies. If not, try using it in conjuction with DVD43 (free) or slysoft anyDVD ($) to bypass the encryptions
If all this sounds like too much effort, just do yourself a favor and pay for one of the tools like ForumMaster said