function addExternalLinks() 
{
    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";
        }
    }
}

function addEventListener(element, event_name, observer, capturing) {  
    if (element.addEventListener) // the DOM2, W3C way  
        element.addEventListener(event_name, observer, capturing); 
    else if (element.attachEvent) // the IE way  
        element.attachEvent("on" + event_name, observer); 
}