Customize the user interface by editing the body of lang/default.html. Functionally, lang/default.html contains three forms, two visible and one hidden:
Username Form (visible)
Password, Login Button (visible)
Login Same Window Form (hidden)
The hidden form is the one that is submitted to the server (POST username and password to login.msc).
You can also insert a new banner, image or link on the Sun Java System Messenger Express Login screen, by editing the lang/default.html file.
lang is the language specific file that you need to edit.