gistfile1.el

(defun explorer (&optional args)
  (interactive)
  (let ((dir (expand-file-name args)))
    (cond ((not (file-directory-p dir))
           (message "%s can't open." dir))
          (t
           (w32-shell-execute "explore" dir)))))
(defun dired-exec-explorer ()
  ""
  (interactive)
  (explorer (dired-current-directory)))
(add-hook 'dired-mode-hook
          (lambda ()
            (define-key dired-mode-map "E" 'dired-exec-explorer)))