var ie = navigator.appName.indexOf('M')!=-1;
var nc = navigator.appName.indexOf('N')!=-1;
var brw_v = navigator.appVersion.charAt(0);

if (ie) {
    fName = "./ForIE5.css";
} else if(nc){
  if (brw_v >= 5) {
    fName = "./ForNC6.css";
  } else {
    fName = "./ForNC4.css";
  }
}

document.write("<LINK REL='stylesheet' HREF='" + fName + "' TYPE='text/css'>");