user registration modification example

add_filter('wpmu_validate_user_signup','nd_validate_user_signup',10,3);
add_filter('signup_extra_fields','nd_extra_fields',10,1);
add_filter('add_signup_meta','nd_add_signup_meta');
add_action('wpmu_activate_user','nd_wpmu_activate_user', 10, 3);

function nd_extra_fields ($result) {
        $first_name = ( isset( $_POST['first_name'] ) ) ? $_POST['first_name']: '';
        $last_name = ( isset( $_POST['last_name'] ) ) ? $_POST['last_name']: '';
        $error_msgs = $result->errors;
        ?>

        <p>
            <label for="first_name">First Name<br />
            	<?php if ( isset($error_msgs['first_name']) && $errmsg = $error_msgs['first_name'][0] ) {
						echo ' <p class="error">'.$errmsg.'</p>';
					}
				?>
                <input type="text" name="first_name" id="first_name" class="input" value="<?php echo esc_attr(stripslashes($first_name)); ?>" /></label>
        </p>
        <p>
            <label for="last_name">Last Name<br />
            	<?php if ( isset($error_msgs['last_name']) && $errmsg = $error_msgs['last_name'][0] ) {
						echo ' <p class="error">'.$errmsg.'</p>';
					}
				?>
                <input type="text" name="last_name" id="last_name" class="input" value="<?php echo esc_attr(stripslashes($last_name)); ?>" /></label>
        </p>
        <?php
}

function nd_validate_user_signup ($result) {
	if ( empty( $_POST['first_name'] ) )
		$result['errors']->add( 'first_name', __('<strong>ERROR</strong>: You must include a first name.','largo') );
	if ( empty( $_POST['last_name'] ) )
		$result['errors']->add( 'last_name', __('<strong>ERROR</strong>: You must include a last name.','largo') );
	return $result;
}

function nd_add_signup_meta($meta) {
    $data = $_POST['first_name'];
    $my_meta = array('first_name' => $data);
    $meta = array_merge($my_meta, $meta);

    $data = $_POST['last_name'];
    $my_meta = array('last_name' => $data);
    $meta = array_merge($my_meta, $meta);

    return $meta;
}

function nd_wpmu_activate_user($userid, $password, $meta) {
    if ( !empty($meta['first_name']))
        update_user_meta($userid, "first_name",$meta['first_name']);
    if ( !empty($meta['last_name']))
        update_user_meta($userid, "last_name",$meta['last_name']);
}