Postcode-postcode distance search function

Hi there im looking for someone to make a script for an asp.net out of the box dating site, here is the site in question whos package is being used for the finished article "http://www.aspnetdating.com/default.htm" the package contains only USA zipcodes this needs to be amended to use UK postal codes, here is how i want the finished article to work.. User inputs their own town/postcode and then selects a radius of how far the search should be from their own location and then provide results back to the user, the finished script should be fully working and include all uk counties,towns and cities and postcodes,