if(navigator.appName=='Netscape' || navigator.userAgent.indexOf("Opera")!=-1){
    document.writeln ('<link rel=\'stylesheet\' href=\'css/nn.css\' type=\'text/css\'>') ;
}else{
    document.writeln ('<link rel=\'stylesheet\' href=\'css/ie.css\' type=\'text/css\'>') ;
}