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));
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_win   = ((agt.indexOf("win") != -1) || (agt.indexOf("16bit") != -1));
var is_win95 = ((agt.indexOf("win95") != -1) || (agt.indexOf("windows 95") != -1));
var is_win16 = ((agt.indexOf("win16") != -1) || (agt.indexOf("16bit") != -1) || (agt.indexOf("windows 3.1") != -1) || (agt.indexOf("windows 16-bit") != -1));
var is_win31 = ((agt.indexOf("windows 3.1") != -1) || (agt.indexOf("win16") != -1) || (agt.indexOf("windows 16-bit") != -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_mac    = (agt.indexOf("mac") != -1);
var is_mac68k = (is_mac && ((agt.indexOf("68k") != -1) || (agt.indexOf("68000") != -1)));
var is_macppc = (is_mac && ((agt.indexOf("ppc") != -1) || (agt.indexOf("powerpc") != -1)));