How to use ajax to show php in a modal pop up

$('a.poplight[href^=#]').click(function() {
 var popID = $(this).attr('rel'); //Get Popup Name
 var popURL = $(this).attr('href'); //Get Popup href to define size

 //Pull Query & Variables from href URL
 var query= popURL.split('?');
 var dim= query[1].split('&');
 var popWidth = dim[0].split('=')[1]; //Gets the first query string value

 //Fade in the Popup and add close button
 jQuery('#' + popID).fadeIn(200).css({ 'width': Number( popWidth ) });


 //Define margin for center alignment (vertical   horizontal) - we add 80px to the height/width to accomodate for the padding
 var popMargTop = ($('#' + popID).height() + 80) / 2;
 var popMargLeft = ($('#' + popID).width() + 80) / 2;

 //Apply Margin to Popup
 jQuery('#' + popID).css({
     'margin-top' : -popMargTop,
     'margin-left' : -popMargLeft
 });

 //Fade in Background
 $('body').append('<div id="fade"></div>'); //Add the fade layer to bottom of the body tag.
 $('#fade').css({'filter' : 'alpha(opacity=80)'}).fadeIn(); //Fade in the fade layer - .css({'filter' : 'alpha(opacity=80)'}) IE

 return false;


});

 //Close Popups and Fade Layer
 $('a.close, #fade, .cancel').live('click', function() { //When clicking on the close or fade layer...
     $('#fade , .popup_block').fadeOut(function() {
         $('#fade, a.close').remove();  //fade them both out
      $('form').clearForm();
 });
     return false;
 });

<a href="#?w=480" rel="whatever" class="poplight"><input type="button" class="button" value="update"/></a>