Before you can start using PHPGTK, you need to download the appropriate files. The PHPGTK team has set up a nice Web site at http://gtk.php.net. The PHPGTK Web site has downloads and documentation for the GTK extension.
Before You Install
PHPGTK still has not reached the 1.0 version, and as such I wouldn't recommend that you use this version of PHP on your production Web server. In fact, there really isn't a reason that you'd want to install PHPGTK on your production Web server. It is a client-side application!
PHPGTK is a developers' toy at the moment, and anything is subject to change, at least before PHPGTK reaches version 1.0. Have some fun with it, try it out, but don't base your company's next big product on PHPGTK 0.5.0. ...