I'm not familiar with how to use xml.arc but this is what I came up with for finding the links on a page:

  (def find-links (str)
    (with (start 0 acc nil)
      (whilet p (posmatch " href=" str start)
        (= start
           (+ p (if (in (str (+ p 6)) #\' #\") 7 6)))
      (push (cut str start (pos [in _ #\' #\" #\> #\space] str start))
            acc))
      (rev acc)))

  (w/url u "http://www.google.com/"
    (find-links u))