This is very odd. I have a Geforce 6800GT, running the latest drivers, and a Samsung Syncmaster 172x LCD monitor (connected by DVI) and it seems I am unable to get resolutions of over 1024x768 in some games - in the game options it tells me the maximum resolution is 1024x768. In most of the games, I've managed to get 1280x1024 (the native res of my screen) in the games working fine, but not in some titles, and this is starting to annoy me greatly, as I know they all support this resolution.

Games I cannot get resolutions of above 1024x768 on that I know support it (they work fine on my laptop with an ATi card.)
-No One Lives Forever 2
-Command and Conquer Generals
-Lord of the Rings: Battle for Middle Earth
-Battlefield 1942
-Rollercoaster Tycoon 3

Other games, such as UT2004, HL2 and Doom 3 work fine, and all the above games except for Battlefield I have managed to get running at 1280x1024 with ini tweaks. This also happens on my Dad's computer, with a Geforce FX5200 and whatever drivers came with it when he got it mid-last year.

This problem has me stumped right now, any solutions? Thanks.