How to display the content with animation ?

How to display the content with animation ?

HI,
i have a <div> control whose content is changed asynchronously through a ASP.NET AJAX Request.
How can i show the display of content with animation , e.g., when the content is added in that div , it should display with sliding down animation , and if contents are disappearing then a sliding up behavior should come .
How can i implement this behavior ?
 
Thanks