I am running an AMD1700 @2gz, with a radeon 9200 and like everone else trying to get better frame rates, didn't run to badly on default settings but chugged a bit with clouds. Thought I'd need to get a new graphics card, however put another half gig of memory in (pc2700) making 1 gb in total and WOW, what a difference, will now run at 30 to 40 fps with Everything at max (including 8 lights, max mipmap, massive global textures, 100% traffic and so on) I reckon it tripled my fps.
Totally transformed the game!
So imho the best thing one can do before anything else is increase the ram to at least 1gb.

Paul
Ps, tried it with everythig on default and got frame rates to go above 100fps at times,
Pps, does anyone know if there is a faster pci card than the fx5200 out there?
system: amd1700 running @2.00 ghz, 1 gb pc2700, radeon 9200 agp Nvidia fx5200 pci, 80 gb hd, 20gb hd, 20gb hd 3x 21" dell crt monitors