I know how to install libpq-dev for ubuntu, but I was looking through past questions and I was not able to find out how to install the package for windows. Is there a place to download that package or a place to download an installer for it?
I don't know that there's a "package" for windows exactly but you can download the source code for postgres here: http://www.enterprisedb.com/downloads/postgres-postgresql-downloads and other places.
Download one of the "core" files for the particular version you're looking for. You'll get a tarball that if you expand you'll find a "libpq" folder. Where that should go on your system depends on what kind of development toolchain you're using.