First of all, there is the PonG library. This library takes care of loading the .pong files for your project and rendering them and taking care of all the GConf foo. In the future it will handle other ways of configuration, such as using bonobo properties.
This library is further divided into the main engine, a glade plugin, and a bonobo plugin. The plugin libraries add support for glade and bonobo widgets inside your dialogs to make the creation of dialogs infinitely flexible. They are also transparent for usage. All you have to do is to use the appropriate initialization routines for the plugin, and the plugin is added.