Hi Wumf,
These are my two favorite photoshop books, and I have a bunch:
"Inside Photoshop 7" by Gary David Bouton (He moderates a forum here).
Within the 1000 pages of this book you'll be introduced to all the essential aspects of Photoshop 7. Don't be intimidated by the size of the book. You won't have to read much before you'll have a good basic understanding of the software.
"Photoshop 7 Down and Dirty Tricks" by Scott Kelby
Once you got the basics down, this book is quite fun. It's really just a bunch of tutorials that teach you how to do a lot of cool things.