In message <200202121547.KAA11865@Sparkle.Rodents.Montreal.QC.CA> you write:

|> Given what I know of the X Consortium sample server, I believe I could
|> build a ddx layer that split a single root across two identical
|> framebuffers.  It wouldn't be very performant, though. :-)

AFAIK that is exactly what the xinerama extension (not compiled by
default) of X11R6.3 or higher does.

	Volker