To use navi2ch, put the following into ~/.emacs.

(require 'navi2ch)

To use monafonts with FSF Emacs-21 or Xemacs, put

(cond
 ((and (eq window-system 'x)
       (or (featurep 'xemacs)
	   (and (boundp 'emacs-major-version)
		(>= emacs-major-version 21))))
  (require 'navi2ch-mona)
  (add-hook 'navi2ch-article-arrange-message-hook
	    'navi2ch-mona-arrange-message)
  (setq navi2ch-mona-enable t)))

into ~/.navi2ch/init.el.