When I first started using PC's I brought a couple from Amazon, eg "The complete idiots guide to ....", (fill in the gaps for yourself), and found them very useful. I think the suggestions that I was a complete idiot made me chuckle.
But nowadays I would tend to try online tutorials and see if they could help me. For instance, if you Googled, "Photoshop CS4 tutorials for beginners" you might find a number of online tutorials that are useful.
What would be a good book to help with using photoshop cs4? I looked on boarders and there are a lot of them on the market. Would the Dummies guides really be helpfull?