Joomla blows and so does this book. I quickly ditched this and learned to use an MVC framework to build custom CMS's instead of fitting sites into existing ones. Try the same and reach enlightenment.
This one was nice for a beginner but it felt like the author was confused what he wanted you to know. It skips around alot and he'll refer the wrong chapter when he wants you to review something. I found other books are more useful. But this has nice practice sites he wants you to build.
This book was written with joomla version 1.3 and 1.6 in mind. Joomla is now at 2.5.5 and 3.0 has been announced. The information is old and outdated in the book.