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";
        }
    }
}
window.onload = externalLinks;