Installation of PHP-GTK 2 on MacOS X 10.4 and 10.5 is actually pretty simple, as it can use the latest PHP-GTK installer, which works just like any other Mac installer.
Just follow the screenshots below this text. The installer includes all the pre-requisites required for PHP to run , but the best feature of the installer is that you don't need X to run GTK+ apps, and the theme is by default Quartz-engine powered, which means you get the whole native Mac look.
For those interested in technical details, a complete list of the prerequisites is given at step 2 of the installation. Download the installer at http://www.kix.in/php-gtk2/PHP-GTK-2.0.0.dmg
Well, I guess that's about what's there to say!