Ajax & onUnload

I am trying to create a system that keeps track of which members are online and which are not. The issue I am running into is that I need a method to set the member's status to offline when they close the browser window. It will currently set a members status to offline if they go to a different page, but not if they close the window. The current function is set as the onUnload event of the body:


function onUnloadRequest()
{
xmlhttp = null;

if(window.XMLHttpRequest)
{
xmlhttp = new XMLHttpRequest();
}

else if(window.ActiveXObject)
{
xmlhttp = new ActiveXObject("Microsoft.XMLHTTP");
}
if(xmlhttp != null)
{
xmlhttp.open("GET", "ajx_change_status.php", true);
xmlhttp.send(null);
return xmlhttp.responseText;
}
else
{
alert("Your browser does not support XMLHTTP.");
}
}

The issue I am running into is that I need a method to set the member's status to offline when they close the browser window. It will currently set a members status to offline if they go to a different page, but not if they close the window.
if u want to find out if a browser window has been closed...u can't

Server really needs to do this with a session timeout unless you are polling the server, you can see when the polling stops.

Eric

Do you know of any websites tutorials on either of these topics? I've been googling for a while with no real results.