You should check out ezboard -
http://www.ezboard.com - it's not a script and you don't have to install it on your server though. It's web-based and remotely-hosted, so you don't have to worry about upgrades, bandwidth, server issues, etc. ezboard is truly "ez". You don't have to download any software either - you do everything at the board itself and in your control center.
ezboard is very easy to use - you can have a fully functional and customized ezboard in minutes - no technical or graphical skills are necessary. ezboard is for experts and novices alike. You can make your ezboard message board look exactly like your 4images gallery.
It doesn't support PHP or MySQL though, so you wouldn't be able to integrate your ezboard and your 4images gallery (however, like I said, you could make your ezboard look almost exactly like your 4images gallery).
In my opinion, ezboard is the best message board service out there.
Check it out -
http://www.ezboard.com