Peter,
I'm aware that it's avery high poly model - it's explained in the readme file.
As for making a low poly version, that requires a complete redesign, so it's not something I have the time to do.
However, having said that, my computer specs are similar to yours, and I get 30-45 fps all the time.
I would make sure you check you have DX9 and 40.72 nVidia drivers - these seem to work bect in FS2K2 (for me anyway).
This is the first message I've got about poor framerates, (I thought I was going to get alot, I got 602 emails today!) but it doesn't seem to be that much of a problem for most users, most with a lower-end PC than yours. I would reccomend making sure you have all your setting optimized for FS.
Try
http://www.guru3d.com and
http://www.futuremark.com for help and tips.
Hope that's of some use to you.
Ric B.