href onclick check if user name in database

Hi

On my page:

http://mandatorymarketinginc.com/web/user-super/super-user-create-01.php

I would like the user to click on the "Check Availability" hyperlink and have it check my database to see if username is available or not, while remaining on this page and then display a message saying either "taken" or "available".

I am stumped on this.
Could someone pls point me in the right direction.

Thanks.

AJaX. Easier if you're using jQuery. But if not, you can manually write your xhr, submit in the background and alert the server response. Or have a hidden div appear with the display.