I think there is a phpBB module for PostNuke. I don't know enough about PostNuke to tell you how to install it though.

I did find this page, but it appears the project is no longer under development.

I used to be a loyal PHP-Nuke user, but have since left that CMS behind, in favor of a non-CMS solution to my website needs. Why 'Nuke is really cool, easy to use, and offers tons of options for customization, the simple fact is that the guy who wrote the code didn't even try to make the system secure from hackers. That's why a team of outside programmers would scour over the code and release security patches for it soon after a new version had been released. Even with this group of coders trying to make the script secure, things got missed, and PHP-Nuke was targeted by hackers anyway.

part of the problem was 'Nuke was the biggest CMS on the block. Since more people used it (in comparison to other CMS's), it was natural that hackers would focus their attention on it more. Nevertheless, if the developer had put more time into security for the CMS, it would not have been the open-door for hackers that PHP-Nuke eventually became.

That's why very few people on this board will support PHP-Nuke in any way, since the darn thing was a mess, from a security standpoint. There's a reason 'Nuke was considered the least-protected CMS security-wise, and it wasn't because hackers just felt like picking on it.

I have heard of PHP-Nuke users that installed more than one of the security modules, plus kept their version patched as needed, and they were still exploited by hackers. When I saw that, I removed my PHP-Nuke system (which was using only one security module) and never looked back.

I suggest you do the same. You could try CPGNuke, which I hear is very similar to PHP-Nuke, yet significantly more secure.

I'm finding some nice free xanthia themes and am installing them.  Very easy.  The pnphpbb and the postnuke work well together so far.  Some decent looking themes that will work for finicky me.

Thanks for all your help and advise.  
I'll be back!

Thanks
I still plan on keeping the php-nuke site. It is a local site and don't plan on advertizing it and therefore maybe it will stay safe.   I have a back up and if it happens I am hoping I can just do the manual reinstall and use the backup from an older date. I keep all my old backups.  If I get hacked it would problably be a good time to check that function out. Right?

I am hoping I can use some of the blocks from my php-nuke site or mabe convert them somehow.  I was using a flash/clock-calendar that I want to use on the post-nuke site.  I haven't even had the time to check more blocks and modules out for the post nuke.  I seen some real nice AT themes but I only know how to install the xathia themes so far. I have downloaded one flash xanthia theme and it works fine on the postnuke.  There are converters out there for AT to Xanthia themes but so far they all want money to do it.  Anyone have the URL to a good xanthia free theme site with alot of good themes?  
I like the administration controls alot better in both post nuke and pnphpbb.  More options I have seen in administration.  It appears that I can edit the files right from the admin instead of using my HTML-kit.  I will problably keep using HTML-KIT for my editing because it gives clean script and no hidden charactors that may mess up script as the editors do that come with Microsoft Windows. Anyway I am use to the HTML-KIT's functions.
Anyone intrested in HTML-KIT feel free to check the site out at Website and download

I think postnuke will be just fine!