Multihead display without a desktop on second monitor

["Frank H. Baker" <vze28dv3@verizon.net>]

I have a 3 head system: one display for the console and two others 
for showing graphics on a clean (unadorned) screen that I control
simply using xlib functions.  This configuration has been working
as prescribed under Mandrake 9.0, but when I tried installing it
on Debian sarg/Linux 2.6, the uniform hatched screen displayed by
X was replaced, after I logged in, by a screen with tool panels 
at the top and bottom on a uniform background.  I have not enabled
Xinerama in XF86Config-4.

Do you have any suggestions how, for instance, to prevent a display
manager from running on the two auxiliary screens or, I guess,
to prevent a session from displaying on them?

Thanks for any help,
Frank Baker