New Count Down Timer Control

Dear Friends
   Hello to all.
   I want a ready-made timer control, in ASP.NET C#, which counts down and then stops at end.    I mean to say that a count down timer control in which I will pass Hours, Minutes & Seconds as parameters    then it should display like (at corner of the aspx page)
 -------------------- |   Session Expires |
|    HH:MM:SS       | --------------------
and when hours, minutes and seconds are zero it should stop.
thanks in advance. Pl. help me