OK, Managed to find out how to make use of the mpp file.
For anyone else who may need to know:
You need to add the 'CS Map installer 98' file to the list of pre-defined templates in MS Project. Do this by opening MS Project, then go to the TOOLS menu and select ORGANIZER. Choose the 'CS Map installer.mpp' file provided by ArchiCAD, then on the left select the Global.mpt file that comes with MS Project. Click on the copy button so the 'Construction Simulation v1' map is copied to the Global.mpt.
When you 'Save as' your MS Project file as a text file, go to choose a map (template) and select the 'Construction Simulation v1'. Now you can open the resulting text file in ArchiCAD under the Construction Simulation menu as described in the Help.
HTH others???
Ricki
Graphisoft Certified ArchiCAD BIM Manager
ArchiCAD 27
Windows 11