var plats = navigator.platform;
var bName = navigator.appName.charAt(0);
var bVers = navigator.appVersion.charAt(0);
var bPath ="";

if(plats == "Win32"){
  if((bName == "N") && (bVers >= 4)){
    bPath = "css/win_nc";
  } else if((bName == "M") && (bVers >= 4)) {
    bPath = "css/win_ie";
  }
} else if(plats == "MacPPC"){
  if((bName == "N") && (bVers >= 4)){
  bPath = "css/mac_nc";
  } else if((bName == "M") && (bVers >= 4)) {
    bPath = "css/mac_ie";
  }
}

if(bPath != ""){
  document.write('<' + 'LINK REL="StyleSheet" TYPE="text/css" HREF="' + bPath + '.css"' + '>');
}