Help with Ajax,Javascript

I need help with PHP-MYSQL-AJAX-JAVASCRIPT fom time to time. This would be a get-paid to be a teacher type of project and eventually maybe be a partner doing some projet part or whole project. Here is my problem: I have a web page generated with PHP with a repport on it. the department manager what this repport to be refreshed every 5 seconds.... for maybe 5-10 person looking at it in real time. the page it filled with content and by itself it makes maybe 20 to 30 MySql query to output de page in 150 ms. I am afraid that refreshing the page every 5 sec will load the Mysql Server with tons of similar request over and over.... I want to track the last change in a Mysql Table with a AJAX querry from the page. then refresh only the repport table div if the reurned value form the Ajax request have changed.. I tried different ways but my knowledge of javascript & Jquerry are insuffisant to make it work. Code: <script language=\"Javascript\"> setInterval(function() { ///here I update a unix stamp every 5 sec .. works. $('#lastupdatetotable').load('[login to view URL]'); }, 5000); /// here i would like to update the <div id=\"tablereservation\"> /// on change of the lastupdatetotable value... but .. that is not the right way to do it ..... $('#lastupdatetotable').change(function(){ $.ajax({ type:'POST', cache:false, url:'[login to view URL]', data:{ userid : [login to view URL], pass : [login to view URL], searchstring : [login to view URL], begin : [login to view URL] }, success: function (html) { $('#tablereservation').html(html); } }); } ); </script> <div id=\"lastupdatetotable\"></div> <div id=\"tablereservation\"><h2>currently updateting table ... </h2></div>