Jan Bodnar has pointed out a great PHP-GTK tutorial on ZetaCode.com that walks you through some of the major points of this graphical frontend for PHP:

This tutorial will teach you the basics of GUI programming with the PHP GTK. The tutorial has 8 chapters which cover the first steps with the library, menus, toolbars, dialogs and various widgets. It has some examples for drawing with Cairo library. The final chapter presents a small computer game; The Nibbles.

Each of the topics has sample code and screenshots of the resulting output for each. Also included is information on layouts and "painting" with Cairo - drawing shapes, rectangles, text, etc.