One final thing. I know a lot of people are uncomfortable asking questions or pointing out mistakes, but this is the first time I've written a tutorial for anything, and the scope and magnitude are such that I absolutely need feedback. My goal is to help people's work. I'm bound to stumble in a few places, and won't take any personal offense if you drop me a note saying "Such-and-such is unclear" or "you need to rewrite x" or "x doesn't seem to work." I'd much rather have someone tell me that something's screwed up, than to have 101 people get upset and give up. Paul