Monitor resolution forcibly changed after resuming from sleep whenusing KVM - how to fix?

Hello,

I put the computer to sleep using the Sleep option on the Vista start
menu. I then, at a later time, wake up the computer.
If the KVM switch is currently set to this PC Windows will resume
normally and the login screen appears.
If the KVM switch is set to my other PC Windows will resume and the
login screen appears. However once I login Vista changes the monitore
resolution from the monitor's native 1680 x 1050 to 1280 x 960.
Presumably the KVM switch doesn't provide the same list of video modes
via ESSID as the monitor.

So my question is:
How do I stop Vista from changing the resolution? OR How do I get
Vista to _automatically_ switch the resolution back to 1680 x 150 when
I switch the KVM back to this PC?

I am using Windows Vista Ultimate with an ATI Radeon X1300 series
card. The VGA output from the card is plugged into an Aten KVM switch.
The VGA output from the switch is plugged into an Acer X223W
widescreen monitor.

Regards,
Chris