It doesn’t need any plugins.What we need is just a code.
The steps are as followed:
1.download the guestbook,then create a notepad,copy and paste the code in the notepad.save it as guestbook.php
2.upload it to the default theme directory.
3.Create a new page under admin control panel,modify the name of page as “Guestbook”,choose the page template as “guestbook”.
Be sure to addlow comments so that visitors can leave words.