While poking around the disks in my linux box, I found my materials for a session on extending PHP that I originally gave as a 3 hour tutorial at PHP{Con West 2003.

Sadly, I seem to have lost the working C code (libares bindings for PHP), but all the relevant parts can be found in the comprehensive PDF I made from the slides: Extending PHP Slides (PDF). The content is based on PHP 4, but should still be applicable to PHP 5.

As it happens, Mike Wallner has recently built his own PECL extension for libares, which is much more complete (and complex) than my examples.