browser_version= parseInt(navigator.appVersion);
browser_type = navigator.appName;
if (browser_type == "Microsoft Internet Explorer" && (browser_version >= 4)) {
           
document.write('<link rel="STYLESHEET" type="text/css" href="style.css">');
} 
else if (browser_type == "Netscape" || "Mozilla" && (browser_version >= 4)) {
document.write('<link rel="STYLESHEET" type="text/css" href="style.css">');
}