http://dev.joomla.org/content/view/1136/79/

Joomla! Developer Network - Development information and resources for Joomla!, In this tutorial, we will go through the steps of creating a joomla template. Joomla is an open source Content Management System (CMS) that is freely (literally) available and supported by a large on-line community. Specifically, we will create a template that uses cascading style sheets (CSS) to produce a layout without use of tables. This is a desirable goal as it means that the template code is easier to validate to World Wide Web Consortium (W3C) standards. It will also tend to load faster, be easier to maintain and perform better in search engines. We will discuss these issues in detail later in the tutorial.