Hi Gowri,
You should take a look at the following forum thread for something very similar to this:http://ko.infragistics.com/community/forums/t/68674.aspx
The only real difference is that the sample on that forum does not use MVVM so everything is done in code behind. All you have to do, though, is take that code and place it into a Behavior<T> and you can keep MVVM. I attached an updated sample that puts everything into a behavior.