I've downloaded the US zip code list from USPS.  This is a very large table.  The database is split with the tables that get updated on a Document Center in SharePoint.  I'd like to have the main tbl_ZipCodeList as a local table and have a Document Center list for any manually added zip codes.  My thought of the workflow is:

User enters a zip code.  Access searched tbl_ZipCodeList for the specific zip code.  If it exists then City, State and Country is added to the specific record.  If it doesn't, the user is prompted to enter the information.  That info is written to the document center table, say tbl_ZipCodeRemote and that information is then written to the record.  That information is then appended to the local tbl_ZipCodeList and ultimately removed from tblZipCodeRemote.