Penitum 4 2.66GHz "Northwood", 640MB Ram, XFX GeForce FX5200. i was talking about CoD2, Serious Sam II was giving really poor frame rates, even on 640x480, despite Serious Engine being spectacular, it's highly unoptimized. actually, there isa Command, which let's you run HL2 in DX9 Mode, you have to modified the shortcut, i didn't tried it, since the game already plays smooth on FX5200.
@icecoolz: The GeForce FX cards default to the DirectX 8.1 rendering path, which runs faster but with fewer visual details. Specifically, there is bump mapping on fewer objects, detail objects are not drawn out to as far a distance, shadows aren't as soft, and water isn't as realistic, this the nasty trick Source Engine performs, so unless some one owns, a High End Graphics card, like X800XT or GeForce 6800x Half Life 2 will run in DX8, unless it'sa ATI Radeon Cardoffcourse, i remember seeing Half Life 2 OEM Ads with 9600XT! it's unfair, but what can gamers, do
on the other hand, you could just try running them in DX9 and expirence a incredible performance hit
or a better solution, just buy a new High end graphics card!