Why I want to underclock:
I'm working on a new build and my old system is going to be my dad's birthday present (because it hurts me to watch him edit photos on a duron). I'm carrying my 8800gt over to my new build, but I have an old X1950 pro hanging around that I'm planning on putting into my current system when I give it to him. My dad won't be doing any gaming. And sadly it's not a graphics integrated motherboard.
The x1950 pro is a bit of an energy hog, so I was wondering if it could be downclocked to use less energy and produce less heat. Would doing this affect stability in any way?
There will be a point where the clocks are too low and will cause issues, but this varies from chip to chip. Halve the frequency and see if it is noticeably cooler and still capable of some 3D, for stability checking, take it from there.
Undervolting it is also an option, but I don't recall this being a software-controlled thing for an x1950, more likely a pencil mod.
I've run my 9600GT down to 300MHz from 650, 1.10v to 0.95v. This drops temps from 42 at idle down to 35.
It's probably not worth the effort and will probably wind up costing you a few bucks, but you could try to eBay the card (or sell it some other way) and then pick up a new modern low end card that will run cooler, quieter, and much more efficiently (from a power standpoint). Otherwise I have nothing to really add.