function openInNewWindow() {
  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") == "newWindow") {
      anchor.target = "_NEW";
    }
  }
}
window.onload = openInNewWindow;