(add-to-list 'vm-mime-type-converter-alist
'("text/html" "text/plain" "lynx -force_html -dump -stdin"))

Inline text/html by emacs-w3m display failed:
(error "Emacs-w3m of this version does not support
Emacs 23; try the development version")

(load-library "mm-decode")
(setq mm-text-html-renderer "lynx")

text/html handling controlled by a new variable
    `vm-mime-text/html-handler' which is set to 'auto-select by
    default.  It causes VM to locate the best library among
    emacs-w3m, external w3m, w3 and lynx to display html
    internally.  (This replaces the earlier variable
    `vm-mime-use-w3-for-text/html'.)