I first tried reinstalling via the recover facility. It copied data (to somewhere), requested the install DVD, then barfed with a "The unattend answer file contains an invalid product key" message. I bailed at that point and did a simple boot-from-the-DVD reinstall, which appears to be progessing nicely. So far I have been unable to locate the data supposedly saved by the recover process, but I've got my own copy -- I think -- and should be fully restored in a couple of hours.
Update: Actually took about 4 hours all told. A lot of files I thought I had saved on an external drive turned out not to be there, plus several other oddities make me glad that I did a clean reinstall. We'll be tweaking things like Office parameters forever, but we're back in business. Somewhat disappointed that whatever caused all this got by MSE. Oh, btw, the Administrator account is behaving itself, although the amount of stuff that even the Administrator can't see or do in Win 7 is frustrating.