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") == "externo")
      anchor.target = "_blank";
  }
}

window.onload = externalLinks;

function popup(link) {
  window.open(link,'status=no,resizable=no,scrollbars=no,menubar=no,width=300,height=400,left=15,top=20') ;
}