First you need to know the format of the video/audio. GSpot can do most formats. Free, here:
http://www.videohelp.com/tools/GSpot
VirtualDub can extract the audio from most containers. If the video will load, you're in business. Free, here:
http://www.videohelp.com/tools/Virtualdub_1.3c-ASF
Open VirtualDub. Click File -> Open Video File. If it loads: Audio -> Full Processing. Audio -> Compression -> PCM (uncompressed). File -> Save WAV. (WAV/PCM is uncompressed audio such as you have on an audio CD).
I'm not on my regular video editing computer, and it's very early in the morning, so maybe the steps above aren't exact.

Good luck and post back with result.