This tutorial tells you about the differences between PHP-GTK 1 and PHP-GTK 2: What has changed, what's new and what not to do anymore.

PHP-GTK 2 tries to be backward-compatible as possible, but as GTK 2 itself broke BC pretty often, PHP-GTK 2 can't do magic. There are many things which haven't changed, but some important smaller changes you have to know when migrating to the second version.