where does Alt become Meta?

[Will Parsons]

I use Emacs on a variety of systems and circumstances, and on just about
all of them I'm used to using the Alt key as Meta, so I was surprised 
recently to find that in an Emacs session running on FreeBSD, but accessed
on a Windows system via TightVNC, A-q was unbound.  Esc-q was bound as
expected to fill-paragraph, but since I find the Alt combinations a lot
more convenient, I would like to fix that, but have no idea where to look.
Where does Emacs map Alt combinations to Meta combinations?

- Will