Is there a way I can review Guestbook entries before they are shown publicly?

Yes. You can enable the Post Approval feature for your Guestbook service, and this will give you a chance to approve the messages before they are made public.

1. Log into your Bravenet account
2. Make sure you are on the Dashboard
3. Click on "Guestbook" in your list of Web Tools
4. Click on "Service Settings"
5. In the "Security Settings" section next to "Enable post approval?" choose "Yes" from the drop down menu
6. Click the "Save Changes" button ant the bottom of the page