This RGtk package is an interface to Gtk.  As such, it allows one to
do in the S language what one can do with Gtk in any other language
for which there are bindings. For the most part, there is a one-to-one
mapping from the C-level routines provided by Gtk to R functions.
Hence, to find out about these functions and what they do
one should look at the Gtk documentation. There are reference
pages for each of the widgets and the general topics 
as well as _tutorials_, etc.  which are available at
  http://www.gtk.org

Additionally, there are currently a few books on Gtk
that I am aware of. 

 Gtk+ Programming in C, 
  Syd Logan
  http://www.amazon.com/exec/obidos/ASIN/0130142646/ref=pd_sim_books/104-2258217-5695136

 Gtk+/Gnome Application Development,
  Havoc Pennington, New Riders.
  http://www.amazon.com/exec/obidos/ASIN/0735700788/ref=pd_sim_books/104-2258217-5695136

 Developing Linux Applications with Gtk+ and GDK
  Eric Harlow, New Riders.
 
There are also several books that I have not seen:
  Beginning Gtk+ and GNOME,
   Peter Wright

 Gnome/Gtk+ Programming Bible
  Arthur Griffith, 

 Sams Teach Yourself GTK+ Programming in 21 Days


All of these relate to programming in C, and not in a higher-level
language such as S. However, they provide the necessary information
for using Gtk, regardless of the particular language.
