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"
});