How do I create an alert("") after user have made a new post?

[dt~]

Hi all,

I wish to alert the user when he/she have reached a new post count as soon as a new post was made. For example, After a user have clicked "send message", he gets a "Congratulations! you have reached 50 posts and your new rank is now XXXX" message box.

Kindly advise a solution for me.

Thanks!
(aka)

http://img101.imageshack.us/img101/1821/catsmile6jx.gif