Images load from the wrong dir

First of all I want to say that this is the best & coolest guestbook I've tried so far. Ik like it so much that I've chosen this guestbook to use on my website.

I only have one problem...

and I hope someone can help me out here. I already used the search option on this forum but I didn't find anything that could solve my problem.
The guestbook works great, but only if I acces it by IP address like http://255.255.255.255/guestbook/, and not by a domain name. I have my own domain name, and I wanted to use a subdomain like http://guestbook.mydomain.nl for my guestbook. The guestbook is running on my server in a dir called /guestbook/
When I configure my web server to send requests for http://guestbook.mydomain.nl to the dir called /guestbook/ on my webserver, then it won't load the images from the correct dir. What happens is that it wants to load the images from http://img/smileys
This is wrong because it should be http://guestbook.mydomain.nl/guestbook/img/smileys. I've been searching through all the files and I didn't find anything where I can set my base URL. Because I thought that might help, or at least be worth a try. Or does anyone know some other way to solve this problem?

Thnx in advance...
Greets, Andre from Holland

open the configuration file config.inc.php

and change the base url

$GB_PG["base_url"] = "http://http://guestbook.mydomain.nl/guestbook";

Thnx
I will try it out..
Let's hope it works.