function openWinCentered(wurl,wname,wwidth,wheight,features) {
	// tatsaechliche breite und hoehe des bildschirms (aufloesungsabhaengig)
	var screenwidth = screen.availWidth;
	var screenheight = screen.availHeight;
	// linke obere ecke des neuen fensters
	var xstart = (screenwidth - wwidth) / 2;
	var ystart = (screenheight - wheight) / 2;
	// properties aus features, fenstergroesse und -position zusammensetzen
	var wprops = "width=" + wwidth + ",height=" + wheight + ",left=" + xstart + ",top=" + ystart + "," + features;
	// neues fenster oeffnen
	var win = window.open(wurl,wname,wprops);
}