a module, or soemthing that will return all of US congressional representatives based on zip code?

I am a semi nuwbie... and I thin that this is a multistep quesiton.
does anyone know of a way that, based on zip code, there is a service that will return a list of congressional representatives, ideally in some kind of xml format?

second question, what would be the best strategy to do this kind of thing? which modules would I be using?

Finally, I want to automatically update some fields after the zip code has been entered. this information would then become part of an accounts profile ( as a separate node ).