Drupal has an well thought-out system for storing different kinds of data in a node structure. I'm sure many coders have looked at a Drupal site and wondered why many had some kind of "node/123456" in the URL. The answer to many other questions about just how Drupal organizes information is covered in the first two chapters. In case you're wondering, yes, readers should be familiar with basic PHP as there's quiet a lot of it spread through-out the book. While this book isn't about programming Drupal's API, the information here is useful as you look to develop themes or create your own types of content.
As you'd expect, the meat of this book is how to create themes. Like other books on theming, it starts off with installing and then modifying starter-themes and builds from there. There is coverage of tools such as Firebug and the Theme Developer module and chapter three also covers some Mozilla Firefox plug-ins to help theme developers. One area designers sometimes avoid is theming Drupal's forms because of their complexity, in the book, forms are given their own chapter. Unlike Packt's Drupal 6 Themes, there isn't much coverage of older Drupal versions except for the section on migrating themes in chapter three, where they provide a 7-item check-list to convert Drupal 5 over to 6. WordPress and Joomal! are given similar treatment, including tables listing the equivalent to Drupal files in other CMS' themes. If nothing else, it gives readers a bit of an idea of the thinking behind different CMS. Theming makes up the main part of the book and pretty much every aspect from modifying to converting existing themes to Drupal is covered.