isNS4 = (document.layers) ? true : false;
NS4 = (document.layers);
IE4 = (document.all);
ver4 = (NS4 || IE4);   
isMac = (navigator.appVersion.indexOf("Mac") != -1);
var platform = navigator.appVersion;
isUNIX = (platform.indexOf("X11") != -1) ||
  (platform.indexOf("Linux") != -1) ||
  (platform.indexOf("SunOS") != -1) ||
  (platform.indexOf("IRIX") != -1) ||
   (platform.indexOf("HP-UX") != -1);
   
if (isMac) {
	document.write('<link rel="stylesheet" href="style/style_mac.css" type="text/css">');
}else if (isUNIX) {
	document.write('<link rel="stylesheet" href="style/style_unix.css" type="text/css">');
}else {
	document.write('<link rel="stylesheet" href="style/style_pc.css" type="text/css">');
}