var agt=navigator.userAgent.toLowerCase();
    var is_major = parseInt(navigator.appVersion);
    var is_minor = parseFloat(navigator.appVersion);
    var is_nav  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1)
                && (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
                && (agt.indexOf('webtv')==-1));
    var is_nav2 = (is_nav && (is_major == 2));
    var is_nav3 = (is_nav && (is_major == 3));
    var is_nav4 = (is_nav && (is_major == 4));
    var is_nav4up = (is_nav && (is_major >= 4) && (is_minor>4.05));
    var is_navonly      = (is_nav && ((agt.indexOf(";nav") != -1) ||
                          (agt.indexOf("; nav") != -1)) );
    var is_nav5 = (is_nav && (is_major == 5));
    var is_nav5up = (is_nav && (is_major >= 5));
    var is_ie   = (agt.indexOf("msie") != -1);
    var is_ie3  = (is_ie && (is_major < 4));
    var is_ie4  = (is_ie && (is_major == 4) && (agt.indexOf("msie 5.0")==-1) );
    var is_ie4up  = (is_ie  && (is_major >= 4));
    var is_ie5  = (is_ie && (is_major == 4) && (agt.indexOf("msie 5.0")!=-1) );
    var is_ie5up  = (is_ie  && !is_ie3 && !is_ie4);

    var is_mac    = (agt.indexOf("mac")!=-1);
    var is_win95 = ((agt.indexOf("win95")!=-1) || (agt.indexOf("windows 95")!=-1));
    var is_win98 = ((agt.indexOf("win98")!=-1) || (agt.indexOf("windows 98")!=-1));
    var is_winnt = ((agt.indexOf("winnt")!=-1) || (agt.indexOf("windows nt")!=-1));
    var is_win32 = (is_win95 || is_winnt || is_win98 ||
                    ((is_major >= 4) && (navigator.platform == "Win32")) ||
                    (agt.indexOf("win32")!=-1) || (agt.indexOf("32bit")!=-1));

    var is_v4 = ( (is_win32 && is_ie4up) || (is_nav4up && (is_mac || is_win32)) )