I can't change monitor resolution in gnome

[Charles Blair <c-blair@uiuc.edu>]

   My monitor is supposed to have an optimal resolution of
1080 by 1240 (or something like that).

   I have installed the testing (etch) distribution with the default
gnome interface.  I have tried clicking on "Preferences" and
"monitor resolution", which brings up what looks like a suitable
screen.  However, I can't get any choice other 480 by 640.
Clicking on the up and down arrows to the right of the number doesn't
do anything.  I can make the number highlight in blue, but can't
over-write it.