Maybe it's as simple as running the Nvidia monitor detection on both,
or getting the latest and greatest drivers for your graphics card. I
have a Dell 22" WFP (widescreen flat panel) and under Ubuntu 8.04 it
immediately drives the monitor at 1680 x 1050 @ 75 hz, the monitors
max capacity, through DVI. Meanwhile the drivers negotiate 1024 x 768
om TV-0. This is all because I downloaded the latest and greatest
from Nvidia.

I also downloaded everything for the EMU10K chip (Soundblaster stuff)
and it drives my soundcard (X-Fi Audio Extreme) better than the
windows drivers do, but with fewer bells and whistles.