In the Advanced Guestbook forum, th eone dedicated to Advanced guestbook questions, the first thread is called Adding a simple human verification test.
The guestbook was not designed to be included like that. If you want to include it in a page like that have a look at Lazarus. The link is in my signature.
Never having used AP I couldn't say. If the AP installer is anything like the AG installer then there is no risk as you re required to input your database details. I don't know what the misc directory contains.
if you have already installed it via cPanel then the database already exists. You do not need to run the install file. Just use the guestbook as normal.