Ok, what in the hell am i doing?

I'm running the Xenarc off of a Nvidia mx440 card at 600 x 800 resolution. If i run it at 60 hz, the screen shifts to the right cutting off half of the screen. If i run it at 75 hz, it come back to center but doesnt look very good.
From my searching I have discovered that the native res is not 600 x 800? So i want to use something else? Can anyone lead me in the right drection?