I'm running it on a P2-350, Win98, 192 megs ram, Voodoo3 graphics card, and a AudioPCI 64V sound card. The game runs just fine for Standard size maps, the longest wait I have between turns is about 10 seconds or so in the Modern Age with the map fully settled. I haven't tried any larger map yet since Standard is sized almost perfectly for me at this point.
I do have some game instability from the older hardware (neither Voodoo3 nor the soundcard were made with DirectX 8 in mind, with the Voodoo I'm using 3rd party drivers) but it's not major, about 1 crash every 15-20 hours of game play.