Thanks to bug #199993:
gnome-display-properties wasn't working with my displays (1680-1050 laptop, and 1440x900 external LCD monitor which is used while the laptop is docked). (It was only allowing me to clone the desktops, and wouldn't fire up the external display unless the wind was blowing right). With Gutsy, I used some shell scripts, and just need to add the Display subsection to xorg.conf, with the Virtual size for my dual setup to work again.
With a little side of applesauce...
©2006 Shannon Eric Peevey