You don't mention what perl version you have, but the following are available via ppm for perl-5.12, either from the ActiveState repo, or the trouchelle repo (or, in some cases, both):
DBD::PgPP,
Pg::CLI,
Pg::Explain,
Pg::Loader,
Pg::Priv.
I don't know anything about Postgres, but I would think that it's the first in that list that gives you the driver you need. So, start with:
ppm install DBD-PgPP
and then 'ppm install' the others if they might also be useful.
Cheers,
Rob