It's probably a driver problem. Try the latest or other versions of the nVidia driver.
A 8800 is capable of a lot more - from click here: Maximum Digital Resolution: 2560x1600 Maximum VGA Resolution: 2048x1536
These statements don't quite add up? "I am changing my monitor to a 23 inch. and need a card that will support 1920x108 res." "My current monitors manufacturer recommended optimum resoltion is 1920x1080."