I guess not.

It should be built into the default install of xorg, although I don't really know how it works in Slackware. It's called mga in xorg.conf. I don't know if installing the official driver messes anything up. I know the official nvidia driver screws around with stuff that a video driver has no business screwing with (the kernel).

It would also appear the mga driver only supports Xorg up to 7.0. Not 7.2 which is what Slackware 12 calls 1.3.

I've been messing with the official nvidia driver, after long using the open source nv driver (which doesn't work very well but it adequate for basic needs). I discovered that the official nvidia driver ignores custom modelines and other xorg.conf settings, if the Mode name is anything like a "standard" resolution name. I found a workaround for it--using a custom Modeline with a name I made up. I changed it from "1280x960" to "1280x960ijk".

With "1280x960", the nvidia driver ignored my desired settings and always used 1280x960p at 85hz. With "1280x960ijk", I was able to use a custom modeline.

So, if your video driver has similar behavior, it might be possible to use the same workaround. Instead of calling your resolution "1440x900", call it "1440x900cyph". Here's a modeline to try out:

In your Mode lists, include "1440x900cyph" and no other resolutions.