function isMac() {

   // convert all characters to lowercase to simplify testing
	var agt=navigator.userAgent.toLowerCase();

	// *** BROWSER VERSION ***
	// Note: On IE5, these return 4, so use is_ie5up to detect IE5.
	var is_major = parseInt(navigator.appVersion);
	var is_minor = parseFloat(navigator.appVersion);

	// Note: Opera and WebTV spoof Navigator.  We do strict client detection.
	// If you want to allow spoofing, take out the tests for opera and webtv.
	var is_nav  = ((agt.indexOf('mozilla')!=-1) && (agt.indexOf('spoofer')==-1)
				&& (agt.indexOf('compatible') == -1) && (agt.indexOf('opera')==-1)
				&& (agt.indexOf('webtv')==-1) && (agt.indexOf('hotjava')==-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_nav6 = (is_nav && (is_major == 5));
	var is_nav6up = (is_nav && (is_major >= 5));
	var is_gecko = (agt.indexOf('gecko') != -1);


	var is_ie     = ((agt.indexOf("msie") != -1) && (agt.indexOf("opera") == -1));
	var is_ie3    = (is_ie && (is_major < 4));
	var is_ie4    = (is_ie && (is_major == 4) && (agt.indexOf("msie 4")!=-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_ie5_5  = (is_ie && (is_major == 4) && (agt.indexOf("msie 5.5") !=-1));
	var is_ie5up  = (is_ie && !is_ie3 && !is_ie4);
	var is_ie5_5up =(is_ie && !is_ie3 && !is_ie4 && !is_ie5);
	var is_ie6    = (is_ie && (is_major == 4) && (agt.indexOf("msie 6.")!=-1) );
	var is_ie6up  = (is_ie && !is_ie3 && !is_ie4 && !is_ie5 && !is_ie5_5);

	// KNOWN BUG: On AOL4, returns false if IE3 is embedded browser
	// or if this is the first browser window opened.  Thus the
	// variables is_aol, is_aol3, and is_aol4 aren't 100% reliable.
	var is_aol   = (agt.indexOf("aol") != -1);
	var is_aol3  = (is_aol && is_ie3);
	var is_aol4  = (is_aol && is_ie4);
	var is_aol5  = (agt.indexOf("aol 5") != -1);
	var is_aol6  = (agt.indexOf("aol 6") != -1);

	var is_opera = (agt.indexOf("opera") != -1);
	var is_opera2 = (agt.indexOf("opera 2") != -1 || agt.indexOf("opera/2") != -1);
	var is_opera3 = (agt.indexOf("opera 3") != -1 || agt.indexOf("opera/3") != -1);
	var is_opera4 = (agt.indexOf("opera 4") != -1 || agt.indexOf("opera/4") != -1);
	var is_opera5 = (agt.indexOf("opera 5") != -1 || agt.indexOf("opera/5") != -1);
	var is_opera5up = (is_opera && !is_opera2 && !is_opera3 && !is_opera4);

	var is_webtv = (agt.indexOf("webtv") != -1); 

	var is_TVNavigator = ((agt.indexOf("navio") != -1) || (agt.indexOf("navio_aoltv") != -1)); 
	var is_AOLTV = is_TVNavigator;

	var is_hotjava = (agt.indexOf("hotjava") != -1);
	var is_hotjava3 = (is_hotjava && (is_major == 3));
	var is_hotjava3up = (is_hotjava && (is_major >= 3));

	// *** JAVASCRIPT VERSION CHECK ***
	var is_js;
	if (is_nav2 || is_ie3) is_js = 1.0;
	else if (is_nav3) is_js = 1.1;
	else if (is_opera5up) is_js = 1.3;
	else if (is_opera) is_js = 1.1;
	else if ((is_nav4 && (is_minor <= 4.05)) || is_ie4) is_js = 1.2;
	else if ((is_nav4 && (is_minor > 4.05)) || is_ie5) is_js = 1.3;
	else if (is_hotjava3up) is_js = 1.4;
	else if (is_nav6 || is_gecko) is_js = 1.5;
	// NOTE: In the future, update this code when newer versions of JS
	// are released. For now, we try to provide some upward compatibility
	// so that future versions of Nav and IE will show they are at
	// *least* JS 1.x capable. Always check for JS version compatibility
	// with > or >=.
	else if (is_nav6up) is_js = 1.5;
	// NOTE: ie5up on mac is 1.4
	else if (is_ie5up) is_js = 1.3

	// HACK: no idea for other browsers; always check for JS version with > or >=
	else is_js = 0.0;

	// *** PLATFORM ***
	var is_win   = ( (agt.indexOf("win")!=-1) || (agt.indexOf("16bit")!=-1) );
	// NOTE: On Opera 3.0, the userAgent string includes "Windows 95/NT4" on all
	//        Win32, so you can't distinguish between Win95 and WinNT.
	var is_win95 = ((agt.indexOf("win95")!=-1) || (agt.indexOf("windows 95")!=-1));

	// is this a 16 bit compiled version?
	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_winme = ((agt.indexOf("win 9x 4.90")!=-1));
	var is_win2k = ((agt.indexOf("windows nt 5.0")!=-1));

	// NOTE: Reliable detection of Win98 may not be possible. It appears that:
	//       - On Nav 4.x and before you'll get plain "Windows" in userAgent.
	//       - On Mercury client, the 32-bit version will return "Win98", but
	//         the 16-bit version running on Win98 will still return "Win95".
	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_os2   = ((agt.indexOf("os/2")!=-1) || 
					(navigator.appVersion.indexOf("OS/2")!=-1) ||   
					(agt.indexOf("ibm-webexplorer")!=-1));

	var is_mac    = (agt.indexOf("mac")!=-1);
	// hack ie5 js version for mac
	if (is_mac && is_ie5up) is_js = 1.4;
	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)));

	var is_sun   = (agt.indexOf("sunos")!=-1);
	var is_sun4  = (agt.indexOf("sunos 4")!=-1);
	var is_sun5  = (agt.indexOf("sunos 5")!=-1);
	var is_suni86= (is_sun && (agt.indexOf("i86")!=-1));
	var is_irix  = (agt.indexOf("irix") !=-1);    // SGI
	var is_irix5 = (agt.indexOf("irix 5") !=-1);
	var is_irix6 = ((agt.indexOf("irix 6") !=-1) || (agt.indexOf("irix6") !=-1));
	var is_hpux  = (agt.indexOf("hp-ux")!=-1);
	var is_hpux9 = (is_hpux && (agt.indexOf("09.")!=-1));
	var is_hpux10= (is_hpux && (agt.indexOf("10.")!=-1));
	var is_aix   = (agt.indexOf("aix") !=-1);      // IBM
	var is_aix1  = (agt.indexOf("aix 1") !=-1);    
	var is_aix2  = (agt.indexOf("aix 2") !=-1);    
	var is_aix3  = (agt.indexOf("aix 3") !=-1);    
	var is_aix4  = (agt.indexOf("aix 4") !=-1);    
	var is_linux = (agt.indexOf("inux")!=-1);
	var is_sco   = (agt.indexOf("sco")!=-1) || (agt.indexOf("unix_sv")!=-1);
	var is_unixware = (agt.indexOf("unix_system_v")!=-1); 
	var is_mpras    = (agt.indexOf("ncr")!=-1); 
	var is_reliant  = (agt.indexOf("reliantunix")!=-1);
	var is_dec   = ((agt.indexOf("dec")!=-1) || (agt.indexOf("osf1")!=-1) || 
		   (agt.indexOf("dec_alpha")!=-1) || (agt.indexOf("alphaserver")!=-1) || 
		   (agt.indexOf("ultrix")!=-1) || (agt.indexOf("alphastation")!=-1)); 
	var is_sinix = (agt.indexOf("sinix")!=-1);
	var is_freebsd = (agt.indexOf("freebsd")!=-1);
	var is_bsd = (agt.indexOf("bsd")!=-1);
	var is_unix  = ((agt.indexOf("x11")!=-1) || is_sun || is_irix || is_hpux || 
				 is_sco ||is_unixware || is_mpras || is_reliant || 
				 is_dec || is_sinix || is_aix || is_linux || is_bsd || is_freebsd);

	var is_vms   = ((agt.indexOf("vax")!=-1) || (agt.indexOf("openvms")!=-1));
	
	if (is_mac || is_macppc) {
		return true;
	}
	else {
		return false;
	}
}