zip_codes.us.mysql

I'm building a directory and have created a (CCK) content type that collects location info using Location and Gmap. I have a lot of entries and would like to auto-populate the city and state fields in the location input by providing just the zip code . Is this possible or would there be a module out there that might do this?

I have created the zip code table in the data base using the zip_codes.us.mysql file that's included with the location module.