Link
I looked around a bit, and found the entire lecture on video at the Carnegie Mellon site (1 hour, 45 minutes). This link is Windows Player format.
Also can be seen on Google video.
It's nice to think that we are now living in an age where tens of thousands of people can see him do this lecture whenever they want, and will be able to do so long after he's gone.
Another short piece on him here.