In case it helps someone, I found these very interesting articles about IMGUI (Immediate Mode GUI) systems (which I am using in my game):

http://www.johno.se/book/imgui.html
http://sol.gfxile.net/imgui/index.html

and a forum about IMGUs
http://www.mollyrocket.com/forums/viewforum.php?f=10

cheers,
Paul