"1680x1050";

Tribes1 ... new monitor.

$pref::VideoFullScreenRes = "1680x1050";

does not seem to be working?

No it does not. :\

I tried tribes with a 22" wide screen with a GeForce 7300LE card. I installed
the latest nvidia driver.

Tribes showed the wide resolution under the video options, I selected that
and it worked fine. Had to move some of the hudbot huds around but
otherwise only a bit of graphics weirdness when looking down on certain
textures from certain angles.

Tell us about your graphics card and your driver.

It will do some widescreen resolutions, but not 1680.