Form Validation against database - Dreamweaver CS4 Spry

Hi all,

I'm trying to figure out how to implement a form validation of some fields, let's say a username. I have a form that inserts on MySQL table, and when the user is typing the username, after it looses the focus on field, validate it if there is a record on table with the specified username. If so, validation will fail.

I already saw something similar with this on Dreamweaver MX using some extension (because at that time, it did not support ajax).

Kind regards, and thanks in advance.