http://ajax.net-tutorials.com/controls/timer-control/

Timer controls allow you to do postbacks at certain intervals. If used together with UpdatePanels, which is the most common approach, it allows for timed partial updates of your page, but it can be used for posting back the entire page as well. Here is a small example of using the Timer control. It simply updates a timestamp every 5 seconds.

http://ajax.net-tutorials.com/controls/timer-control/