function open_center(thislayer){

	if (is_nav){
		if (is_nav4up) {
		   	var layerRef="document.layers";
	 	   	var styleSwitch="";
		}
		if (is_nav6up){
			var layerRef="document.getElementById";
	    		var styleSwitch=".style";
	  	}	

		// Berechnung der Mitte
		var breite = window.innerWidth;
		var hoehe = window.innerHeight;
		var left = 263;
		if (breite > 890){
			var tbreite = breite - 890;
			tbreite = tbreite /2;
			left = left + tbreite;

		}
		if (hoehe > 629 && is_nav6up){
			left = left + 5;
		}
					  
		if (is_nav6up) {
			document.getElementById(thislayer).style.left = left;
		}
		else {
			eval(layerRef+'["'+thislayer+'"]'+styleSwitch+'.left="'+left+'"');
		}
	}

	else if (is_ie4up) {
		
		var breite = document.body.offsetWidth;
		var left = 263;
		if (breite > 890){
			var tbreite = breite - 890;
			tbreite = tbreite /2;
			left = left + tbreite;
			document.all[thislayer].style.left=left;
		}
	}
}