You can use built-in Emacs function ‘w32-shell-execute’ to execute an MS Windows system function.

Library w32-shell-execute.el provides command ‘w32-shell-execute-verb’, which gives you an interface to ‘w32-shell-execute’ that tries to make it more convenient to execute MS Windows Explorer verbs that are available for the current file or directory.

And here is an alternative, for use in Dired:

(defun w32-dired-open-explorer ()
  "Open a file in dired mode by explorer.exe as you double click it."
  (let ((file-name (dired-get-file-for-visit)))
    (if (file-exists-p file-name)
	(w32-shell-execute "open" file-name nil 1))))

;; Bind it to `o' in dired mode.
(define-key dired-mode-map "o" 'w32-dired-open-explorer)

CategoryWThirtyTwo MsShellExecute WThirtyTwoFileAssociations