As somebody who just bought a Mac this year after being an HP snob for years, I can tell you that there is a learning curve when you go to using the Mac. This Switching to the Mac guide helps you make a smooth transition. This book will teach you how to transfer your stuff, assemble Mac programs so you can do what you did with Windows, and learning your way around Mac OS X. Everything you did on a PC, you can do on a Mac. The program may just have a different name.
Even though I figured out a lot of this myself, I would have loved to have this book. I even learned a few new things reading Switching to the Mac. Honestly, this should be a required purchase when you buy a Mac! It'll make the change a lot less crazy for you!