I think the way most property portals do it is by way of using an xml data feed that is formatted in accordance with certain guidelines. The feed is then imported for automatic updating. We do it by way of an excel spreadsheet that lists the information such as State, City, Property Type and so on. The user then goes to their account area where they can import the fields. Basically, a table is generated and the user selects the field type and then imports the listings. I hope that assist you.