Use this to remove the titelbar of the jQuery dialog and not the close button
 $(function() {
    $( "#dialog" ).dialog();
    $("#ui-dialog-title-dialog").hide();
    $(".ui-dialog-titlebar").removeClass('ui-widget-header');
 });
for newer version jquery UI > 1.10.3
$("#dialog .ui-dialog-titlebar").css({ 
     "background-color" : "transparent", 
     "border" : "0px none" 
});