function Is() {
        var 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) && (agent.indexOf('opera')==-1)));
        this.ns2 = (this.ns && (this.major == 3));
        this.ns3 = (this.ns && (this.major == 3));
        this.ns4b = (this.ns && (this.minor < 4.04));
        this.ns4 = (this.ns && (this.major >= 4));
        this.ie = (agent.indexOf("msie") != -1);
        this.ie3 = (this.ie && (this.major == 2));
        this.ie4 = (this.ie && (this.major >= 4));
        this.op3 = (agent.indexOf("opera") != -1);
        this.win = (agent.indexOf("win")!=-1);
        this.mac = (agent.indexOf("mac")!=-1);
        this.unix = (agent.indexOf("x11")!=-1);
        this.dom = document.getElementById?1:0;
        this.ns6 = (this.dom && parseInt(this.major) >= 5 && this.ns)?1:0;
      }
	
      is = new Is();
	
      if (is.ns6) {
         doc = "document.getElementById";
         sty = ".style";
         htm = "";
         abrir = "(";
         cerrar = ")";
      }
      else if(is.ns4) {
        doc = "document";
        sty = "";
        htm = ".document";
        abrir = "[";
        cerrar = "]";
      } 
      else if(is.ie4) {
        doc = "document.all";
        sty = ".style";
        htm = "";     
        abrir = "[";
        cerrar = "]";
      } 
      else {
        doc = "";
        sty = "";
        htm = "";
      }

function cambiaColorCapa(idCapa, color)
{
  capa=eval(doc+abrir+"'"+idCapa+"'"+cerrar+sty);
	capa.background=color;
}