Yes number one you can set it in the admin wo were you have to approve all the comments. Number 2 you can make it so they need a password to post a comment. Number 3 by any chance do you still have a copy of AVG still running on the same server. If so disable it. Delete ann the AVG files.
You might want to upgrade to Lazarus guestbook it has all the features you want. And here is the numerical ips for rogers.com 64.71.246.156 , 64.71.246.28 , 24.153.22.14 , 24.153.22.142 Just remember this link here is your friend. http://www.networksolutions.com/whois/index.jhtml
You can go into your admin section and delete them one at a time. Or go to your phpmyadmin in your cpanel and batch delete them. Or you can switch to Lazarus Guestbook and not worry about spam near as much.