As promised in my Date input and calendar popup article, here are instructions.
In the head section of your page add the following lines.
<link type="text/css" href="calpopup.css" media="screen" rel="stylesheet">
<type="text/javascript"script src="events.js"></script>
<type="text/javascript"script src="calpopup.js"></script>
<type="text/javascript"script src="dateparse.js"></script>
<script type="text/javascript">
// Optionally change the date format.
// g_Calendar.setDateFormat('dd-mm-yyyy');
</script>
Because of a Safari bug with onclick events in elements that are created using createElement and insertBefore DOM methods, if you want this to work in Safari, add the following div right after the body tag. It does not affect other browsers to add this here, it just means that you have to add HTML to your page that should be created with javascript.
<body>
<div id="calcontainer"></div>
Add an input field to your form with a class of "dateparse".
<input type="text" size="10" id="dateField" class="dateparse">
Add a button or an image with an onclick event to access the calendar popup.
<a href="javascript:void(0);"
onclick="g_Calendar.show(event, 'dateField')"
title="Show popup calendar">
<img src="calendar.gif"
class="cp_img"
alt="Open popup calendar">
</a>
The only required items for the show method are event and the id of the date input field.

Here's the sample date parser and calendar popup.
Update: 3 May 2006 Forgot to check for mdyyyy when parsing a date from an input field. Fixed now.
Update: 22 Jul 2006 Added ability to set the drop down year menu to any start at any year.
Update: 3 Aug 2006 Added instructions on how to make click events work in Safari.