True, perhaps turn down the settings? What's the best game he can run? Maybe we can see how powerful it is by comparing it to games that have worked.
[Edit]
Crysis seems to be a good benchmark for the graphics performance on newer cards, there is a Crysis Demo available, so it might be worth a shot. Pressumable, if it can handle Crysis, even on lowest settings, then I'd assume it'd have little trouble with Left4Dead. (I run left 4 dead on high and Crysis Medium)
--The hatred of those who harbour such ill feelings as, "He reviled me, assaulted me, vanquished me and robbed me," is never appeased.--