Mint comes with envy, so to get the latest nVidia or ATI driver you just log out to a terminal and type "envy"
Do you have "nVidia X server settings" under System tools in Mint menu? Have you tried to set the values there?
If not - use envy. If you have that option and it doesn't help you have to edit xorg.conf. Move to etc/X11 and open xorg.conf Look at Section "Screen" and the resolutions you have there.
If 1024 x 768 is max, just add the resolution(s) you want.
Look at Section "Monitor" and the values for VertRefresh
You probably have to change that to something like 43 - 60