if ((navigator.appVersion.indexOf("Mac") != -1)) { 
document.write("<link rel='stylesheet' href='stylesheet/mac.css' type='text/css'>");
}
else if ((navigator.appName.indexOf("Netscape") != -1)) { 
document.write("<link rel='stylesheet' href='stylesheet/win_nn.css' type='text/css'>");
}
else { 
document.write("<link rel='stylesheet' href='stylesheet/win.css' type='text/css'>");
}