Here's a link of him talking about Alzheimer's:
http://www.youtube.com/watch?v=Z44ip5kYQ8w
(I was about to post a link about him on religion, too-- I'm sure Sir Pratchett will remain an atheist in his foxhole, and implying that his convictions are shallow enough to be changed simply by "bad times" is an insulting slur)
http://www.youtube.com/watch?v=8qqnTmBTwOo