datepicker help, how to make the calendar popup?

i'm using jquery 1.5.1 and jque开发者_高级运维ry-ui im trying to create a simple html page with input field and a button that when pushed a calendar will popup.

JS

   $( "#datepicker" ).datepicker({
            showOn: "button",
            buttonImage: "images/calendar.gif",
            buttonImageOnly: true
        });

Markup

<p>Date: <input type="text" id="datepicker"></p>

Reference

http://jqueryui.com/demos/datepicker/#icon-trigger