Hi David,
If your addresses are geocoded, then you can create a trade area around the point. The Trade Area can then be joined with your addresses using the spatial match tool to get all points contained in that trade area.
If you don't have addresses but have spatial objects for your zip codes, then you can build the trade area and use the spatial match to match the Zip Code spatial objects with the trade area spatial object.
Both thesse solutions require you to have the zip codes represented somehow. I don't see how it would be done if you don't have the zip codes reprented somehow.
