Here's a hook function that will hide the References header in
VM's mail-mode buffers.  This is for Good 'Ol Emacs only; this
won't work under XEmacs.  You will notice the cursor behaves as
if the References header is still there... that's because it is
still there.

(defun hide-references-hook ()
  (save-excursion
    (let (lim)
      (goto-char (point-min))
      (re-search-forward (concat "^" (regexp-quote mail-header-separator) "$"))
      (setq lim (match-beginning 0))
      (goto-char (point-min))
      (cond ((re-search-forward "^References:.*\n\\([ \t].*\n\\)*" lim t)
	     (let ((o (make-overlay (match-beginning 0) (match-end 0))))
	       (overlay-put o 'invisible t)))))))

(add-hook 'vm-mail-mode-hook 'hide-references-hook)

Here's the XEmacs version of that function.  Required change was
replacing make-overlay with make-extent, and overlay-put with
set-extent-property.

(defun hide-references-hook ()
  (save-excursion
    (let (lim)
      (goto-char (point-min))
      (re-search-forward (concat "^" (regexp-quote mail-header-separator) "$"))
      (setq lim (match-beginning 0))
      (goto-char (point-min))
      (cond ((re-search-forward "^References:.*\n\\([ \t].*\n\\)*" lim t)
	     (let ((o (make-extent (match-beginning 0) (match-end 0))))
	       (set-extent-property o 'invisible t)))))))