Lorna Mitchell has an introduction to Zend_Db, the Zend Framework database abstraction layer posted to her blog today:

I recently worked on a project which was based on Zend Framework - I haven't worked with it before and I was temporarily confused by the existing implementation of some of the database-level stuff. After much reading and untangling of code, I'm now pretty clear how this should look, so here's my overview. I'm not going to go into setting up a whole application, but this is a quick primer on how data models go together.

She talks about table modeling, fetching rows/data from the model and working with rows/rowsets.