function check_my_online_time()
{
 	try {
		req = window.XMLHttpRequest?new XMLHttpRequest(): 
		new ActiveXObject("Microsoft.XMLHTTP"); 
	} catch (e) {
		//Kein AJAX Support
	}


	req.open('get', 'community/check_online.php');
	req.send(null);
}

check_my_online_time();
setInterval("check_my_online_time()",45000);