Keith, in order to have all the resolution available you need to install the latest monitor INF drivers. This will interact with the VBIOS of the graphics controller and the monitor EDID (monitor BIOS) as well as the latest graphic drivers and latest BIOS for your system.
Also make sure you are using straight cables.
If you get to performed all my recommendations and the issue persisted, please provide a dxdiag report from your system to get further details on the computer being used. To get this report, go to the Start menu, type dxfiag and then click on "Save all information"
Thanks for the quick reply. I see now that my original question was faulty. The monitor in question indeed has a native resolution of 1680x1050, and not 1680x1024 as I originally thought. Sorry to take up your time.
No problem at all Keith.!