Thanks to both Paul and James--I tried both methods, and this time, of course it worked!(I'd have sworn that I used Paul's method, but I couldn't make it work until I posted a question--why is that?!)
However, I asked the wrong question.
What I really want is a gedcom that has my great-grandparents, but also ALL their collateral relatives (no descendants)--brothers, sisters, aunts, uncles, etc., etc.I can't figure out how to get all those people into a gedcom from the generation of eight great-grandparents and beyond.
I suspect this has to do with filtering in the Project Explorer, but I seem to be unable to think in those terms.Any help appreciated!