>> How dated has the book become with the release of NT v6?
Not much at all. It's dated in the sense that it doesn't cover everything that's available, then again it doesn't cover everything that is in NT5 either.
It's designed as a "tutorial" - so getting you familiar with the environment - what all the terminology actually means, how it all fits together and so on. If you feel like you're not understanding the big picture then I strongly recommend this as a place to start.
just like going from Dos to Windows was a change, and some stuff had to be unlearned, so Windows to Web is also a change (but a much bigger one) and the key is in identifying "how it works". the templates do a good job of presenting the familiar Clarion paradigm, but under the hood things are really quite different.
cheers
Bruce