Framerate problem

[kilikol1]

I have this (reserve) PC that runs semi-modern games, like MW1 and CSS, quite happily (>50fps) with fpsconfigs on 1920x1080. But when it comes to this game, I get estimately 20-35 fps, no matter where I look. The osd-display of Afterburner doesn't work on this game, so I suppose that Windows won't run the game in 3D-mode. When I tried the game on a school computer (you know, integrated gfx, some A64 single-core, Vista), it ran fluently. I tried to search for the solution, but it seems to be to run the game in 800x600 and windowed mode. Well, that didn't change anything (surprise surprise, the game lags even more on higher resolutions).

My specs are:
XP
X1950GT (OC:ed quite a bit)
Sempron 3000+
1GB of ram
(And other hardware at the same level)

So is there anything I could do (besides trying another OS)?
Thanks in advance!

[Enari]

This game uses software render, that means that it only uses the CPU.
and from what i can tell the Sempron 3000+ have a clockrate of 2000–2200 MHz
You should be better of when the OpenGL client get released.