User to complete Zip Code and flash return city name (XML)

I have a list of zip codes and city names that correspond to each zipcode. What I need:

To create a XML file, and make flash to read it and return the city names.

It will be in a form, with 2 inputs: user inputs the zip code on the first input field, and on the second input (city name) the name will be filled. All the zip codes have 4 digits so I guess it is a good thing. Does anybody has any tutorials of source code to help me since I do not have large experience with AS3.

Thanks