1. I used the Gibbed VPK Extractor to read the .VPK files Valve uses to store game content.
2. Launch the extractor and browse to C:\Program Files\Steam\steamapps\common\portal 2\portal2
3. The extractor should only see one file; the 'pak01_dir.vpk' package.
4. Begin extracting, but I recommend creating something like a 'Portal 2 Content' folder on your desktop and using it as the output destination.
5. Go make a sandwich, as the extraction took something like 5 minutes on my machine. (This is the part that generates an extra 5gb or so of content.)
6. Once completed, browse to the extracted files. Feel free to delete everything except the 'sound' folder as most of it is files you probably can't open anyway.
7. Everything is in .wav format, so if you want to convert anything you'll need a program like Audacity.
8. I've found the VO doesn't play in Winamp, which leads me to believe very small files either aren't read properly or Winamp just doesn't like them. However, every file plays file in Audacity. (Can get tedious, and I'm sure there's a faster way.)