The game ran pretty smooth on my father's pc during beta:
AMD Athlon 900
512MB PC 133 Ram
AOpen Geforce2MX 64MB (one of the first ones out, not the lower end ones)
Graphics aren't the nicest. And it can get a lil choppy in some areas but usually fps stays stable around 26, peaked at 40 in certain areas.
But main rig that runs it really smooth is:
AMD Athlon 64 3200+
1Gig DDR400
ATI Radeon 9800Pro 128MB.
Even with Max vid settings, max rez and everything turned on in the drivers, the game doesn't even hiccup.
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Ps. Yes I'm an AMD/ATI guy!