I really did not like MS Windows before reading this book. I prefer a UNIX-based OS, and I could care less for the Windows OS, but this book explains how to tweak everything. Not only the looks of Windows (the boot screen, the logon screen, your icons, the start button, etc.), but also performance modifications that can decrease the boot time and overall performance of your OS. It also gives tips on how to secure the system from spyware programs, viruses, etc. Most of these tips can be implemented for free (even the anti-virus software)! The book is well-written and easy to follow; I highly recommend it.
[Since the publishing of this review, Steve Sinchak has written a guide to Windows 7. -- SL ]