I have a GF6600, 512MB of RAM, and a 2400 processor. I turn off anti-aliasing and set the detail level to "normal," and it barely lags, except when zooming in or out!
But the most interesting thing is that my friend has a GF 7800GT, 1024MB of RAM, and a 3200 processor, and it lags just as much as mine!
Maybe it's not the computer, but the game itself that's acting up?
Also, the operating system can affect performance. Maybe your friend has had Windows for two years:)
