My book, PHP and MySQL 24-Hour Trainer, was released in October 2011 by Wrox. The intended audience is for people who know HTML/CSS and want to try programming. PHP & MySQL are the basis of many open source content management systems, including Joomla, Drupal and Wordpress.
I gave a presentation on how to program Joomla modules at Joomla Day NYC in October 2011 that is recorded at http://www.ustream.tv/recorded/18039338. The files used for the examples can be downloaded at https://github.com/andreatarr/Joomla-Day-NYC/download.
Learn how to write your own custom modules with this tutorial I wrote for the online Joomla! Development Beginner's Guide at http://cocoate.com/jdev/module. This is based on the same examples from the video.