We're just starting to look at heating and cooling systems (it has
neither, tho does have gas lines which were used for wall heaters).
I've called a few places who will come out to give us estimates, but we
have no idea where to really start with what *type* of systems are
available. Google searches yield 1000s of sites, but I thought I'd ask
here for some advice.

I don't have one, but I like the looks of Durham (www.durham.com)
Duo-rad hydronic system. (Which is a radiator and fan combination
through which you pipe either hot or cold water, depending on the
season.)