I think dgvoodoo fetches video-resolutions from DirectX. Can you add 1680x1050 in your video-drivers as a custom resolution?

I remember a while back that I was unable to select 1280x960 in Hidden & Dangerous 2, but in Windows I had that resolution. So I added 1280x960 to the Forceware-drivers as a custom-res, then I was able to select that res in-game.
I don't know the capabilities of ATI's drivers though.