I would suggest searching the forums for similar topics like this one:
http://4homepages.de/forum/viewtopic.php?t=1658Any topic that discusses user integration with 3rd party message boards, like phpbb, would be a good place to get started. It is up to you to find a pre-built chat solution that suits your needs and one that you can integrate with 4images.
Best of luck.
By the way, I checked
www.phpbb.com and found that someone has provided a mod to use phpMyChat in phpBB. I know there's work that's been done to integrate 4images users with phpBB so maybe that's an avenue to explore.