function Is ()
{   var agt=navigator.userAgent.toLowerCase()
    this.major = parseInt(navigator.appVersion)
    this.minor = parseFloat(navigator.appVersion)
    this.ns  = ((agt.indexOf('mozilla')!= -1) && ((agt.indexOf('spoofer')== -1) && (agt.indexOf('compatible') == -1)))
    this.ie   = (agt.indexOf("msie") != -1)
    this.win   = ( (agt.indexOf("win")!=-1) || (agt.indexOf("16bit")!=-1) )
    this.mac    = (agt.indexOf("mac")!=-1)
}

var is;
is = new Is();

var os_browser
if (is.win && is.ie) { os_browser = "win_ie"; }
else if (is.win && is.ns) { os_browser = "win_ns"; }
else if (is.mac && is.ie) { os_browser = "mac_ie"; }
else if (is.mac && is.ns) { os_browser = "mac_ns"; }