Custom add user fields

What I want is to add custom user fields in the add user screen in the administrator page. I don’t need to allow this information to be changed by the users as they are for control purposes, like for example suscription end date and similar.
I found several ways of “Editing” the user’s information, but nothing solid for user creation.

All i could remove/add from the “user add” page was the contact methods with this code that i found on a blog post and i can’t credit because i already lost the page:

function remove_contact_method( $contact_method ) {
	// Add Twitter
	$contact_method['twitter'] = 'Twitter';
	// Remove Yahoo IM
	unset( $contact_method['yim'] );
	unset( $contact_method['aim'] );
	unset( $contact_method['jabber'] );
	return $contact_method;
}
add_filter( 'user_contactmethods', 'remove_contact_method', 10, 1 );

Now, I found a way to “pseudo-hack” the “add user” page, i tried to use the code but i didn’t understand it very well:

function adduser_new_fields() {
	if ( !current_user_can( 'add_users' ) )
		return true;
	require_once('class.extrafields.php');
	$html = '
<tr>
	<th><label for="user_address">Direcci&oacute;n</label></th>
	<td><input type="text" name="user_address" id="company" value="" class="regular-text"></td>
</tr>';
	echo "
<script type='text/javascript'>
jQuery( function() {
	if ( jQuery( '#createuser #role' ).length) {
		jQuery( '#role' ).parent().parent().parent().after('"; echo $html; echo "');
	}
});
</script>";
}
add_action('admin_head', 'adduser_new_fields');

function adduser_save( $user_id ) {
	if ( !current_user_can( 'add_users' ) )
		return false;
	update_usermeta( $user_id, 'user_address', $_POST['user_address'] );
}
add_action( 'user_register', 'adduser_save' );

Well, I hope someone can understand what I want to do and probably give me a hand with it.