I hate to double post, but I came up with a work around.  it's not the most elegant solution, but it will work.  I thought I would share it and hope that this will be addressed in the DDRMenu soon.

Open the jquery.dnnmega.js file and add the following lines of code to the bottom of the document.ready function:

    // WORKAROUND: find every anchor that ends with -popup and add target="_blank"
    jQuery('a[href$="-popup"]').each(function() {
        this.target = "_blank";
        this.href = this.href.substring(0,this.href.length -6);
    });

Next, simply add -popup to the end of any link you want this to apply to.

Our team has spent quite a bit of time tweaking the JavaScript, the XSLT, and the CSS to get the DDRMenu working and looking just so with the XSLT template.  Starting over with a new templating engine isn't really an option for us as this point in the project.

Thanks for looking into resolving this within an XSLT template for me.  Seems to me it's something that has been overlooked and should be implemented anyway.