jQuery AJAX polling for JSON response, handling based on AJAX result or JSON content

I'm a novice-to-intermediate JavaScript/jQuery programmer, so concrete/executable examples would be very much appreciated.

AJAX MySQL Polling

I was wondering if someone could help me develop an AJAX/javascript script that will run a PHP script once every 5 minutes sending. This script runs sql query against a mysql table to see if a specific field is 0 or not. if it is not 0, i need it to return to the ajax/javascript function and change the titlebar of the browser with the number.