Simple interface to GDevices?

[psz@lcs.mit.edu]

I have the luxury of a 2-screen Mac to work with, and am trying to
figure out how to let a program get info on things like the following:
	- how many screens are there, really?
	- what are their color/gray, depth, etc., characteristics?
	- where are they in the coordinate system in which windows live?
	- what is the actual GrayRgn?

It seems like GDevices contain such info, but I'd rather learn that
this is already encapsulated in some useful Lisp form than have to try
to figure it out from Inside Mac and lots of trial and error.
Examples or pointers appreciated.