Good book. It really helped me in my first PC build. Thorough description of building a PC. Good description of component selection. I especially liked their overview of cabling. They also did a good job in explaining how to test your components. My only complaint here is their attempt to describe how to test a PSU and the rails on the PSU, using a multimeter. They lost me half way through, which was frustrating because it was a skill I really wanted to learn. It would have been helpful if they had used more pictures and diagrams to describe this procedure.
The book also included a good step by step guide to the PC build, as well as an excellent overview of installing Windows.
I also read their companion book, Build the Ultimate Gaming PC. Although that book didn't have a thorough overview of Installing Windows, it did have a very good overview of other post build procedures including: creating floppy boot discs, setting up Raid and partitions, installing and setting up drivers, optimizing performance, maintenance, benchmarking, etc.
To be honest, it would have been better if they had written just one book. I think the book on Build the Ultimate Gaming PC would have been perfect if they had added the Windows Installation guide they had in this book. Then they could have added a section on component selection for Build the Ultimate Custom PC, or Home Theater PC. They could have called it Build the Ultimate PC. But I guess they'll make more money splitting it up into a few books.
If I had to recommend one book, it would be the other one, Build the Ultimate Gaming PC. It's a more thorough book on the build process, no matter what kind of PC you're building. You can always find online descriptions of Installing Windows. There's an excellent DIY Guide to Building an AMD Socket 939 PC at HardwareZone.com, that includes an excellent description of installing Windows. It was written July 2004 but it's thorough, well written and free.