First, in the Internet there's a good introduction to the ZS:

http://www.onlinephotography.com/bw.html

Not as complete as a book, but a very good jumpstart (and very cheap...).

Second, as a 35mm shooter, I feel the ZS has to be understood, used as a tool but not in the details. Here's how I use it:

- Do the Zone 1 tests as described in the doc above;
- Adjust your development time/dillution so MOST of your photos print in grade 3 paper (for 35mm it seems to be prefered to grade 2).
- Expansion and contractions (see the doc again) will be made by changing paper grades.

Jorge O