The best program for the job would be ImToo DVD Audio Ripper, which can extract the audio from any DVD into a host of different formats. The free trial lets you rip 5 minutes of audio at a time (you could go through and rip an entire DVD this way, but it's time-consuming) and costs $29 if you want to remove the limitation. Other options include Xilisoft DVD Audio Ripper SE and DVD Audio Ripper SE, both of which cost $29 and have 5-minute-per-session trial limitations.

Hope this helps,
John