I’ve written a note on how to do this, which is on a separate page.
www.edubuzz.org was one of the early WordPress Multi-User (WPMU) sites. It started off with Version 1.0 Release Candidate 4 of the WPMU software. The way WPMU encoded tables within the database changed in later versions, and needed changed. This has proved an extremely time-consuming exercise, and the note is an attempt to save others some time if they encounter the same problem.