Becoming an XFCE developer

[Shahar Weiss]

Well, due to my intensive use and admiration towards XFce, I became more 
interested in the way it is built. And so I'd like to try help within 
the project.

And now to the point:

I realize XFce is based on GTK+2, and so it's necessary to know and 
understand GTK. So I was wondering if anyone knows of a good GTK+2 
tutorial, if possible.

Also, are there any other libs in which XFce uses?