To install, run

 lwp-download http://tjmather.com/Geo-PostalCode_19991101.txt.gz
 gunzip Geo-PostalCode_19991101.txt.gz
 ./load.pl
 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.
