Adding popup calendars in a aspx page

here is a good sample to pop up a server calendar control rather than use any javascript calendar control
http://www.15seconds.com/issue/040315.htm

if you want to use javascript calendar.. than check out this cool skinned calendar (dhtml) which can be used...
http://www.dynarch.com/projects/calendar/

There is a Calendar control in AJAX tool kit, it is a perfect one.
How Do I: Configure the ASP.NET AJAX Calendar Control?