Stan Sted,
My advice for minimum FS2000 requirements would be 500MHzP3, 128MB Ram and 16MB Graphics. As far as I can make out (and I have been studying forums daily since October) the most important factor is CPU speed but all three interact so none of the three factors should be below the above specs. I am running absolutely flawlessly on 700MHz, 256MB and 32MB so whilst this is a top end system it can be done.
Great forum exists at
www.microwings.com
Hope this info is of use.