addLoadEvent(externalLinks);

function addLoadEvent(func)
{
    var oldonload = window.onload;

    if (typeof window.onload != "function")
    {
        window.onload = func;
    }
    else
    {
        window.onload = function(){oldonload(); func();}
    }
}

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";
        }
    }
}