His topic will be "Writing Your Own PHP Extensions: How & Why from A-Z" and will be presented as a beginner's guide to creating these expansions on the PHP core. It will explain the "whys" and where to get started as well as some resources and other materials on where to go from there. Some basic code will be provided to get your feet wet and provide a base to work from.
For more information on the talks being given for this year's conference, check out the sessions list and to narrow it down to just the PHP related talks, check out this. Other speakers covering PHP-related topics include Chris Shiflett, George Schlossnagle, Andrei Zmievski, and Rasmus Lerdorf.