To install, run

 lwp-download http://tjmather.com/Geo-PostalCode_19991101.txt.gz
 gunzip Geo-PostalCode_19991101.txt.gz
 ./load.pl        # this will take a few seconds...
 perl Makefile.PL
 make
 make test
 make install

Make sure to install the postalcode.db, city.db and latlon.db files in an approriate
directory.  This will be the directory passed to the db_dir parameter of the new constructor.