I play on my laptop and it has an Intel Pentium Dual CPU 1.5Ghz, 1GB RAM. The actual graphics card? Well that's even more embarassing, it's an integrated chip called the "Mobile Intel(R) 965 Express Chipset Family 250MB.
The salesman told me it was the best integrated chip currently available (Last December) but he's a salesman so I didn't really believe him, it does work like a dream though
I bought a Nvidia 7600GT for my desktop PC but I don't think it's possible to transfer that onto my laptop unfortunately.
The integrated card I do have is quite astonishing really, it allows me to play on maximum setting, with cities and everything on highest setting etc. For an integrated card to be able to do that suprised me a lot, I'm not sure how it's possible for an integrated card to run this nicely, but I don't care how it's done, I just like the look of it