On his blog today Leniel Macaferi has a new post showing how to install PHP on OSX 10.6.5, really enabling the PHP that's already installed.
I hit a pretty good tutorial to enable PHP on Mac at About.com written by Angela Bradley that gets to the point: How to Install PHP on a Mac. Along the way I had to solve only one minor thing described in the caveat section at the end of this post. You see that the title of this post has the word installing (well I thought I had to install it '" that was my first reaction), but in fact it could be the word enabling because PHP is an integral part of Mac OS X Snow Leopard and we just need to enable it as you'll see soon.
He talks about enabling the web server, enabling PHP and testing the installation with a phpinfo. There's screenshots included so you can be sure you're in the right places.