Oh, Derrick, you are the most wonderful!!!
I used the code and - voila - it worked. I must have tried every variation EXCEPT that one!
To explain my reasoning ...
Search engines cannot index pages that are called with a ? in the URL, but it can index the result from *.php. I want to have a unique page for each category, so I can optimize for that category, have it found by a search engine AND have a direct link, with no passed variables, possible.
My existing site category pages are well-ranked and I don't want to loose that. I'll be able to keep them with a 301 permanent re-direct now that I can have a specific, indexable page that the re-direct points to.
Again, thank you, thank you, thank you!
Marie