Over on PHPEverywhere, there's a link to a previously posted article (from DevArticles) about creating custom extensions with C for PHP. Well, unfortunately, that example shows you how to use the Microsoft products to accomplish that goal, but PHPComplete has an alternative.

In this tutorial, they step you through creating an extension on a unix-based system, but it's not quite as easy as it is on the MS side of things. Be prepared to do a lot of tweaking and typing (versus more pointing and clicking), and pulling together a lot of different resources yourself. Other than that, it's a snap to get a small sample extension written and loaded into PHP.

I think that PHP would benefit from more extension being written for it - even ones that may not be "official" in the source code. Classes are nice, but some of the things that they do can get pretty involved and slow - but, drop those into an extension, and you're zipping along, just like PHP was meant to.