displaying ajax modalpopup in c#

Hi!
 i have a simple modalpopup ,label dinded to it.
          Now i have a link button inside repeater controll along with oncommand event, when i click on that link button i want to display some message to user with some value binded to label inside panel of popup..
        after successfull operation i need to display some message so i'm trying to show popup from backend like,
  popupid.show();
  plz help me out..