Hi Frank,
> I am writing a highly-technical review article with a colleague who
> knows only MS Word on the Mac (and so is not particularly
> computer-savvy). I've agreed to use Word, for which I don't much care,
> but it seems to be the only way to go at the moment.
Have you considered Abiword instead? Cross-platform. Source available.
Apparently it has an equation editor.
http://www.abisource.com/
http://cleardefinition.com/oss/abi/blog/2006/09/13/equation-editor-links/
Never used it though.
Cheers,
Ralph.