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) &&
                  (agent.indexOf('webtv')      == -1));
    this.ns2    = (this.ns && (this.major      ==  2));
    this.ns3    = (this.ns && (this.major      ==  3));
    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.ieX    = (this.ie && !this.ie3 && !this.ie4);
}

var is = new Is();