Photoshop CS2 for Digital Photographers by Scott Kelby's a gd place to start. Its gd for beginners.
Secrets of The Digital Darkroom by Peter Cope's also pretty good, though you need some knowledge of Photoshop to really benefit.
BTW you can pick up bks for CS as well. CS2 is essentially the same, but with upgraded features which are quite self-explanatory once you know your way ard.