function Is() {
	    agent  = navigator.userAgent.toLowerCase();
	    this.major = parseInt(navigator.appVersion);
	    this.minor = parseFloat(navigator.appVersion);
	    this.ns    = ((agent.indexOf('mozilla')   !=   -1) &&
	                 ((agent.indexOf('spoofer')   ==   -1) &&
	                 (agent.indexOf('compatible') ==   -1)));
	    this.ns2   = (this.ns && (this.major      ==    3));
	    this.ns3   = (this.ns && (this.major      ==    3));
	    this.ns4b  = (this.ns && (this.major      ==    4) &&
	                 (this.minor                  <= 4.03));
	    this.ns4   = (this.ns && (this.major      >=    4));
	    this.ns6    = (this.ns && (this.major     >=    5));
	    this.ie    = (agent.indexOf("msie")       !=   -1);
	    this.ie3   = (this.ie && (this.major      <     4));
	    this.ie4   = (this.ie && (this.major      ==    4) &&
	                 (agent.indexOf("msie 5.0")   ==   -1));
	    this.ie5   = (this.ie && (this.major      ==    4) &&
	                 (agent.indexOf("msie 5.0")   !=   -1));
	    this.ie55  = (this.ie && (this.major      ==    4) &&
	                 (agent.indexOf("msie 5.5")   !=   -1));
	}
	
	var is = new Is();
	// Inicializa ancho, alto  para posicionar capas dependiendo resolucion pantalla
	// y la captura de teclas, se llama desde onLoad()
	var ancho = 0;
	var alto = 0;
	function Inicializar(){
	    if(is.ns4) {
	        ancho=innerWidth;
	        alto=innerHeight;
			doc = "document";
	    	sty = "";
	    	htm = ".document"
    	} else if(is.ie4 || is.ie5) {
	        ancho=document.body.clientWidth;
	        alto=document.body.clientHeight;
		    doc = "document.all";
		    sty = ".style";
		    htm = "";			
    	}
	}

	function PosicionCapa() {
	    divB1Obj = eval(doc + '["divB1"]' + sty);
	    divB2Obj = eval(doc + '["divB2"]' + sty);
	    divB3Obj = eval(doc + '["divB3"]' + sty);
		var cuenta;
		cuenta = Math.floor(ancho/2);
		cuenta2 = Math.floor(alto/2);
	    divB1Obj.left = cuenta - 150;
		divB1Obj.top = cuenta2 - 85;
	    divB2Obj.left = cuenta + 120;
		divB2Obj.top = cuenta2 - 75;
	    divB3Obj.left = cuenta - 13;
		divB3Obj.top = cuenta2 + 140;
	
	    divB1Obj.visibility = "visible";
	    divB2Obj.visibility = "visible";
	    divB3Obj.visibility = "visible"; 
	}