The second author of this book has certainly been around for a long time (as long as I can remember). I am not familiar with Joli Ballew's other work but she has a considerable number of books to her name. The two authors complement each other and the resulting book is helpful and largely well written for the target readership (identified by the publishers as 'Novice to Intermediate').
If you want some help in keeping your Windows XP based machine working reasonably well this is a fair book for the non-expert. However one piece of advice that I would give most forcefully to anyone who wants to start cleaning his or her machine, tweaking software and editing the registry is to have a complete back-up before you do anything else. Hard drives are cheap enough these days so that there is no excuse for not cloning the drive before you start messing. If you do not do that I can promise you that even if you are an expert you will regret it.