Ravi
There is no easy way to let the server know that the client has closed their browser. The client doesn't make any kind of call to the server to do this, it just does it. You might try something with a small unseen
applet that lets the server know that the applet has been stopped - that's about the only thing I can think of and its not a sure thing either.
Did you try to do a search for this? It's been asked quite a few times before.