These talks are from the first two startup schools, not YC dinners. However, I believe all of them except Wozniak have spoken at YC dinners as well.

These are the dinner speakers this (winter) batch: http://ycombinator.com/w7speakers.html

Tim O'Reilly's talk suddenly turns into the last 10 minutes of your talk at 17:00.

A lot of them may have been from the startup school(s). Sacca, Wolfram, and Woz were speakers at the first startup school, and the dates on the audio files are right after it.

Agreed. The main directory is from the first Startup School, held in Boston (Oct 05). The apr06 subdirectory is from the second Startup School, held at Stanford.