CPU: Dual core 2.0 ghz
There's no need to require a dual-core, it will just work better if you have it.
ATI X800, NVidia 6600 or better
There's no way. I was running Civ 4 on a X800 and it really wasn't that great for the game already. There's no way it will run Civ 5 all that well. And the 6600 is an antique, it's bound to require at least a 7000 series card.