Added the last few submissions to the opening post.
Erluk- I remembered seeing something like that in the default.ini for the full game; sure enough, it was there, and your tweak works for the full version as well as the demo.
I also tried out deadman's Auto-Resurrection cheat. After changing the appropriate line, I went and got myself killed. After a few moments, I got up again, ready for another fight. The only problem was that I was now standing waist-deep in solid rock- coming back to life had dropped me partway through the floor!
Something else I tried was to set the startup movie to the cinematic intro, since someone mentioned it in another thread. This didn't work, though. I can read some movies like the Eidos logo from the Thief 3 installation directory, but not others, like the cinematic intro. The line says ShortIntroMovies- maybe a restriction of some kind on what movies will play?