$('a').each(function() {
   var a = new RegExp('/' + window.location.host + '/');
   if(!a.test(this.href)) {
       $(this).click(function(event) {
           event.preventDefault();
           event.stopPropagation();
           window.open(this.href, '_blank');
       });
   }
});

Or, you can still avoid the validation problems and just append the class target=_blank thing to any links with href attributes starting with http://. The example below only targets links in a #content area. Scoping down like that might be a good idea in case your menus are dynamic and create full URLs.

$("#content a[href^='http://']").attr("target","_blank");