As the Zend Developer Zone points out, there's a great introductory tutorial that anyone should check out if they're looking to get into the world of programming plugins in WordPress.

Wordpress is a highly used and easily customizable platform for content creation and management. In this post I'll guide you through the basic structure and steps required to create a simple and useful wordpress plugin.

Bruno walks through the whole process, from creating the default plugin information, adding filters to the sample code and making the hook so that the WordPress API knows how to use it.