Thanks for the advice.
I managed to do it an alternative way (all in XP):
I downloaded Blender (
http://www.blender.org) and an .acf file importer plugin
(
http://marginal.org.uk/x-planescenery/tools.html, Xplane2Blender).
Then exported to .ac format ( Blender understands .ac in the standard distribution)
This worked well.
Again, thanks for the help.