Error passing serialized array.

Error passing serialized array.

Im trying to pass a form that has an array of Importances in it. I can use the Jquery to pick up the form elements and serialize them, but having trouble pass the 'string' to a PHP script through AJax

    $('#form').submit(function(){
        var impArray = $('#form').serialize();            
           
        var phpScript5 = 'update_KB.php';
        $.ajaxSetup({ cache: true });
        var ajaxPass6 = 'imp=' + impArray;
        var ajax_load5 = '<img src="loading-icon.gif" alt="loading..." />';   
        alert(ajaxPass6);       
        var $display_area = $('#display3');
        $display_area.html(ajax_load5).load(phpScript5, ajaxPass6);

However when i check to see if $_GET['imp'] is posted it returns with a NULL??
When the alert box pops up it displays the sting so why isnt it passing it?
Cheers