the minimeta widget by daniel huesken works with mu when put in the plugins folder, except that it never produces a registration link for new users. Otherwise it’s a very useful widget for customizing your login window. You can find it here: http://wordpress.org/extend/plugins/minimeta-widget/
I add the following code around line 151, which adds a permanent registration link (for those who are not already logged in):
global $user_level ;
get_currentuserinfo();
if (” == $user_level) {
echo ‘<li><a href=”wp-signup.php”>Register</a></li>’;
}