Is it possible to install FSX for the 2nd time on a new harddisk on the same computer, so I can copy some maps to the 2nd FSX?

I have uninstalled FSX and then re-installed it on an external hard drive on the same computer if that helps? If you mean two simultaneous installations on the same computer then I think that might cause a problem. I'm not even sure that is possible.David

Have you tried copying the entire FSX folder to another location on your drive so that you have two installations, then just try running it from either of the fsx.exe files?This works for many other games that I know of, It's done frequently while beta testing some of them.