After speaking to the user again, it appears it was only Office 97 they
had success with, not 2000 as they first though. (Bangs head on wall)

So it's probably never worked beyond that version. I still have the
strange situation of the mail merge working with the spreadsheet in the
'local' folder to the Word Doc, but not in the user's network folder,
so there is still an issue there I need to solve, but it appears that
the version of Office is not the problem.