i, too, got the idea, my gpu was asked to perform actions it's phisycally not able to perform, but as the gpu is newer than the game i discarded that thought.
Note that I said "doesn't know how to do." That's different from being "physically not able to perform." Your GPU is physically capable of anything Undying can throw at it, but other factors may prevent it from "knowing how to do" it. A common cause for this is having outdated drivers, though since you said you have the Forceware's, that definitely isn't the case.
i didn't yet try to install an old driver
I wouldn't bother yet. Remember, you're trying to resolve an anomaly, not squeeze a few more drops of speed out of a stable system.
using directx 9.0c in the first place, i replaced it with 8.1, still getting the same results.
Keep using DX 9.0c.
i think there was no option of changing to opengl at all...
There should be one. Look for an option that says something like "show/hide unsupported renderers;" that should make OpenGL available.
i'm still of the opinion that if my system runs games like mohaa with all details enabled, it should run undying like nothing
There's the way things should be, and there's the way things are. Seriously, if you haven't tried that suggestion, I
strongly recommend trying it. Something is choking your system, and finding a "safe" level of operation is the first step in isolating it. Once you isolate it, you are in a better position to fix it.
american mcgee's alice that, as far as i know, uses the same engine
American McGee's Alice uses the Quake III engine, which uses OpenGL exclusively. Undying uses the Unreal Engine, which uses Direct3D but unofficially supports OpenGL too.