I know, a higher resolution would appear to be available only after a driver-level passage that needs to be done, which differs from Ati/AMD to Nvidia cards. I'm using an AMD here, which needs an external utility (all details here:
http://forums.guru3d.com/showthread.php?t=366244); I don't know about Nvidia, but I think it should be possible to achive through the Forceware (if that's still their name, I'm outdated there) control panel.