Postcode search script enhancement

This is a enhancement of our existing application where users enter a postcode and search for suppliers within a certain radius. Please contact us for access to a demo. The enhancements On the user / searcher side; We would like to enhance the application to allow searchers to select from a list of categories that the returned results belong to. We would also like there to be a second list of 'sub-categories' that appears under the category to further narrow results. When the results are displayed we would like them divided into the labelled categories. Listed nearest to furthest. On the administration side; We would like the administrator to be able to manage the 'categories' & 'subcategories' (add, edit & delete). And also be able to add each entry to each 'category' & 'sub-category'.