Google Map API / map nearest locations

I have a database/list of a few hundred geographic locations (available data includes the street name, cross street, and zip code). All the points plot correctly on a Google map when entered individually. All points are within a 100 sq mile radius. I want for a person (website visitor) to be able to enter a zip code, and then be shown a Google map with the 20 closest locations plotted on the map. If that is possible, please post your bid for coding it. Thanks!