can't increase resolution

In the display settings panel the slider for the screen resolution doesn't
let me select 1600x1200, which I always used on XP. It has everything up to
1280x1024 and 1920x.

I'm running 64bit vista with a radeon x700 card on a GNR cm1997fs monitor.
With the latest drivers for the gfx card, but only using the generic drivers
for monitor as GNR can't be bothered with updating their drivers. I've tried
the generic plug and play, generic non plug and play and the SVGA 1600x1200
drivers that come with windows, to no avail. I have also downloaded an .inf
file suppossedly for vista but it says it can't run on x64.

Does anyone know how to fix this - or how to edit the .inf file so vista
accepts it?

Thanks