"Aus die reihe": Drupal Howto's from IBM; Part 5: Getting started with Drupal "Using open source software to design, develop, and deploying a collaborative Web site"

In this series, the IBM® Internet Technology Group designs, develops, and deploys a closed community Web site using a suite of software that is freely available. If you followed the instructions in the previous articles, you now have a generic Drupal installation. You can begin to add content and modify the style. This article introduces the Drupal programming model used in developing Web sites and includes a description of different types of content, developing new features using modules, implementing hooks to enable those modules, and site URL design.

A rather good howto I must say from a rather cool company IMHO.