On all the forums related to FS2K the same story is as here. The graphics cards are not up to the job.
What I have found is that Voodoo and TNT cards, plus some ATI cards, are causing chaos. The starting point should be getting the latest drivers downloaded from their respective sites.
200mhz will run it, but the Graphics card HAS to be good. You can, if you seek them out, exchange a 200mhz CPU for a higher one.
I use a Matrox Millenium G400 card (currently £85inc VAT ((was higher))) and it suits FS2K perfectly. I get frame rates of over 40-75 with it. I also run a Celeron 400mhz and 128mb of RAM. No more is needed. Certainly not 256mb of RAM!