userAgent = navigator.userAgent.toLowerCase();
n4 = document.layers;
ieWin = (document.all && userAgent.indexOf("mac")<0);
ieMac = (document.all && !ieWin &&   
  userAgent.indexOf("icab")<0);
w3c = document.documentElement;
aol = (userAgent.indexOf("aol")>-1);

if (!ieMac && !ieWin) {						// preload mouseovers
	top = new Image();
	go  = new Image();
	vor = new Image();
	zur = new Image();
	top.src = "../images/nav/top_1.gif";
	go.src  = "../images/nav/go_1.gif"; 
	vor.src = "../images/nav/vor_1.gif";
	zur.src = "../images/nav/zur_1.gif"; }