ZipCodes lookup script

I am looking for a zipcode information lookup script, I would prefer in .php and .txt only, but if needs to be .cgi and MySQL that is acceptable although not my first choice. The goal is to have a form on a front page that someone can type in either a zipcode (and get the city/state) or the city/state and get the zipcode. What this needs to be able to do is be indexable by search engines (hence if you can do a mod_rewrite type job that creates individual files with results that would be able to have targeted ads based on the zipcode and city/state results that would be ideal as well). Results need to have a customizable template. I know most of this code is already public domain, it is the certain characterisitcs that I am searching for necessitate my searching for someone to create this job for me. If you have already created something very similar to this and can show a demo that would help as well. I am developing a series of domains with tasks similar to this one, if you are chosen and the first project goes well, I will have others available that you will be given the right of first refusal on. Any questions, topvar at [login to view URL] .