function addLoadListener(fn){
    if(typeof window.addEventListener !='undefined')    window.addEventListener('load',fn,false);
    else if(typeof document.addEventListener !='undefined')    document.addEventListener('load',fn,false);
    else if(typeof window.attachEvent !='undefined')    window.attachEvent('onload',fn);
    else{
        var oldfn=window.onload
        if(typeof window.onload !='function')    window.onload=fn;
        else    window.onload=function(){oldfn();fn();}
    }
}

addLoadListener(externalLinks);

function externalLinks() {
   if( !document.getElementsByTagName ) return;
   var anchors = document.getElementsByTagName( "a" );
   for( var i=0; i<anchors.length; i++ )
   {
      var anchor = anchors[ i ];
      if( anchor.getAttribute( "href" ) && anchor.getAttribute( "rel" ) == "external" )
         anchor.target = "_blank";
   }
}