This is actually a rather straightforward programming task but only after you know how it all works; understanding either JSON or XML, Perl data structures, and the basic mechanics of Ajax (use a library like jQuery, don't write your own from scratch). If you've never done it I'd say the chances of doing it "ASAP" are slim to none.

Here is a small, standalone CGI + Ajax + Template -- CGI/Ajax example: lookup a value when a field is filled in. It does not meet your requirements but if you can get it running and use Firebug (a Firefox plugin) on it, you might be able to cut your learning curve down drastically. Having a working example helps a great deal when trying to learn this stuff.