Also, for your linking pleasure, I have a few links submitted by arts:
First, a good review of a book that many of you probably already have sitting over on the shelves. For those that don't, this review of Web Application Development with PHP is very good. It gives you a nice look at what's inside the covers and who would really benefit from it.
The second link is a nice intro article on the O'Reilly site that talks about joins and their numerous benefits. It doesn't get too specific, just an intro really...not for the gurus out there.