I have a Dell P4 1.7; Ti4200 w/64 MB of VRAM; and 512 KB of RAM on the MOB. The sliders are set for 50% AI, very heavy or dense as appropriate on the scenery. Cloud cover is set around 65%. Frames are locked at 10 fps and sometimes drop as low as 7 at airports with lots of eye candy . AA is off on the software and on on the card. A few jaggies but not bad at all. The sim runs smooth with no jitters (much better than 2002 in that regard)and I have Norton running in the background.
Would I like a 3 GHz machine w/1GB RAM and a Radaeon 9800 Pro? Sure...if someone was giving it to me. But I flew from KLAX to KLAS with real-time weather updating every 15 minutes and the airport scenes were awesome. Once I landed at KLAS I changed the time to night and my jaw dropped when I saw how gorgeous and realistic the Strip looked.
My point is, you don't need a megasystem to get darn good performance from FSACOF. Maybe it wouldn't have run as smooth if I was flying in a thunderstorm (I'll try that next) but I'm happy as a pig in cool mud with the software.