How can I reimplement external pop-up jQuery code in Prototype?

I have this code in jQuery, that I want to reimplement with the prototype library.

// make external links open in popups
// this will apply a window.open() behaviour to all anchor links
// the not() functions filter iteratively filter out http://www.foo.com 
// and http://foo.com so they don't trigger off the pop-ups

jQuery("a[href='http://']").
      not("a[href^='http://www.foo.com']").
      not("a[href^='http://foo.com']").
      addClass('external');

jQuery("a.external").
      not('a[rel="lightbox"]').click( function() {
      window.open( jQuery(this).attr('href') );
      return false;
});

How can you iteratively filter an collection of elements using an equivalent to the not() operators listed here in jQuery?

From stackoverflow Chris Adams

• The filtering can be done using the reject method like so:

  $$('a').reject(function(element) { return element.getAttribute("href").match(/http:\/\/(www.|)foo.com/); }).invoke("addClassName", "external");
  

  From derfred