Building dynamic functionality into a address entry field (zipcode finder)

Hi all,

I just need some advice to know if the following is worth doing:

I simply would like to integrate the ability for the user of a website I’m developing to type in their zip code and have their city name and state returned.

I imagine this will involve Flash remoting, a server, and some kind of PHP stuff…? I have seriously spent over an hour looking around (here and the web) and have found little on this. There’s stuff out there for a zip code proximity search utility but not much else.