I was trying to upgrade or convert some old Arbortext Interchange import templates to the new Arbortext Import/Export map templates. I searched high and low for this documentation, to no avail (even with Google Desktop!). Eventually I resorted to a support ticket with PTC. To save everyone else some time and trouble, here's the official response:
Instructions for migrating from Interchange to Import/Export can be found on page 216 of the Customizer's Guide(page 228 in the PDF Reader).
And just to be a little more clear, that doc should be in your docs directory (C:\Program Files\Arbortext\Editor\docs\customizing_guide.pdf)