Thanks much. That is exactly what I was wishing for.
I'm by no means the org/emacs expert, but here's what I'd do:
> every third Monday of each month
* Meeting on 3d Monday of each month
<%%(diary-float t 1 3)>
(see
http://www.gnu.org/software/emacs/manual/html_node/emacs/Sexp-Diary-Entries.html
and http://orgmode.org/manual/Weekly_002fdaily-agenda.html)
--
John Rakestraw