there's no way to actually extract the original audio tracks since they're muxed .par files. your best bet is using capture software like snapz pro and make sure your audio capture settings are high. it saves as .mov but you can convert that to an .aif or .wav easily.
Comments
you can do it with DVD Decrypter (Freeware), it's easy just a little work because you need to add the trackinformation for every song.
This Guide should help you and if you have questions just ask.
http://www.dvd-guides.com/content/view/136/59/
badbart