if (document.cookie.indexOf("browser=")==-1)
{
    if (navigator.appVersion.indexOf("Macintosh") > "0") 
    {
        document.cookie = "platform=mac;" + "expires=Sat, 28 Aug 2005 17:34:20 GMT;"+ "path=/;";  
    }
    else 
    {
        document.cookie = "platform=pc;" + "expires=Sat, 28 Aug 2005 17:34:20 GMT;"+ "path=/;"; 
    }
}