function openWindow(windowurl,windowname,w,h) {
		if (!windowurl)
			var windowurl = "kontakt.html";

		if (!w)
			// var w = screen.availWidth;				//dynamic width
			var w = 500;

		if (!h)
			// var h = screen.availHeight-20;		//dynamic height (without taskbar etc.)
			var h = 530;


		leftPosition = w/2;
		topPosition = h/2-150;

		if (!windowname)
			var windowname = 'Kontakt';

		var windowprops = 'width='+ w +',height='+ h +',top='+ topPosition +',left='+ leftPosition +',toolbar=no,location=no,directories=no,status=no,scrollbars=yes,menubar=no,resizable=yes'; //set popup window properties

		var popup = window.open(windowurl,windowname,windowprops); // open popup window with properties
	}