I did something similar to this several months ago - make a selection list change based on what's typed in a text box. Fairly trivial as a matter of fact, I put together http://hackforfood.com/fancy.html in less than an hour. It doesn't do remote lookup, it stores the data on the page itself, but again it's trivial to add the XMLhttp stuff. Since the target audience of this script was non-skilled programmers, I made a simple js interface for them to add choices to the lists and to support multiple selections on the same page.