I think problem is much deeper, than ATI or NVidia. Authors of this game choosen OpenGL way to sieze of available markets except consoles. Minimum moves to get new edition. But at the same time Microsoft and OpenGL is "incompatible", DirectX is king of the ring. And as I've heard, drivers of ATI and NVidia is based on Microsoft version of OpenGL, especionally in new Vista.
Now, me instersting only one question, Frictional Games as developer contacted with manufactors of drivers or not? And what was answer?
ps. sorry for english