9600GSO with spare parts computer

Hey Gunner!  

I'm no expert and someone else may be better qualified to give you a more definitive and knowledgeable answer, but in just glancing over the system requirements for the games you mentioned, I'd say you'd be fine with that setup. You'd meet the recommended specs for both L4D and Civ4 easily, and LOL only makes mention of the 8800, which is a faster card than the 9600GSO if you're talking about the GT 512mb, GTS, or GTX versions, although some sources do chalk up the 9600GSO to a rebranded 8800GS. Even still, you'd be able to run it at very decent quality settings. I'd say you'd be safe running any games with comparable requirements. It also depends on factors such as what resolution you're intending to play at.

Link to a review: http://pcgamingcorner.com/wordpress/?p=420

They used a Core 2 Quad, which will make a difference when comparing it to your Athlon 64 x2, but as you can see, they tested COD4 and L4D and recommended 1680 x 1050 with High Settings as optimal for both of these games under those hardware conditions with your particular card in the mix.