Using a non-preset resolution

I'm trying to set 1280x960, a 4:3 resolution for my 4:3 monitor. It's supported by the card and the monitor, and is what I use under XP.

But it's not one of the monitor's pre-sets, so xrandr doesn't report it, and, even though I have it specified on a "Modes" line in xorg.conf, X uses the pre-set 1280x1024 instead.

Anyone know how to coerce X into using the value in xorg.conf?
Ok, that should support it. If you used the vesa(4) driver you would have been a bit limited. Can you post your /var/log/Xorg.0.log to Pastebin (or a similar service) and provide the link?