$(function(){
		$('#main_cat').change(function(){
			var $mainCat=$('#main_cat').val();
		
						// call ajax
						$("#sub_cat").empty();
							$.ajax({
								url:"http://thematic4you.com/wp-admin/admin-ajax.php",
								type:'POST',
								data:'action=my_special_action&main_catid=' + $mainCat,
								success:function(results)
								{
								//  alert(results);
								$("#sub_cat").removeAttr("disabled");
								$("#sub_cat").append(results);
								}
							});
			}
		);
});