render the game basically unplayable
You might want to look here:
http://www.gamespot.com/features/6140517/p-3.html
In short, you can run XP itself on a minimal system with only 64 meg of RAM and all but absolutely essential services disabled but having time to brew a pot of coffee between actions isn't actually real functional - games optimized for the very latest graphics are quite similar when run on minimalist cards.
Will CoD2 work with the following cards?
NVIDIA GeForce 6150 card
or
Integrated Intel Graphics Media Accelerator 3100
I know there are other forums out there similiar but I just wanted this clear cut answer.

Chowhound
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GameFAQs
GameSpot
Giant Bomb
TechRepublic