Upgraded to Ubuntu 7.10, now resolution stuck at 1600x1200

[Leo Mauler]

I just upgraded to Ubuntu 7.10.  Now the screen
resolution is stuck at 1600x1200.  My monitor is
straining to do this resolution and the screen is all
bendy.  I can't adjust the monitor itself to work with
the new resolution as this monitor is shared between
three other computers and would need to be readjusted
back to the prior settings every time I pressed the
KVM switch.

I have been to System > Preferences > Screen
Resolution. I pull down the menu and select the
resolution which has always worked well, which is
1024x768.  I press Apply.  The screen resolution *does
not change*, but I get a dialog box saying "do you
want to keep this resolution or revert to the old
resolution?"  Selecting "keep this resolution" does
not change the resolution to 1024x768.

I've tried Ctrl-Alt-Shift + to change screen
resolutions.  For some reason 1024x768 is not an
option in the list.

I'm presuming that editing a config file is in order. 
I have no problem doing this and understand the need
to back things up.  However, I have only done XFree86
config files and don't know what to do with xorg.

Incidentally, 1600x1200 has always been the resolution
used by the graphical login screen.  I've wanted to
change the initial resolution to 1024x768 as well, but
I don't know how to do that either.  Frankly I just
hate graphical login screens, but I can't do without
my GUI for normal computer use.

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