It will not mess things up, but incase the next versions of phpbb have had some security fixes and they are not done, then your forums becomes vulnerable to hack attacks.
Ok thank you i decided i was going to use mambo anyway i here its not hard to make phpbb intergrate with it and i also here that some mods would mess up the intergration in phpnuke with phpbb.
if you don't have much on your website i would not worry about it
but if you do have sensative data i agree with the posts above you should use the other.
but integration wise you should not have a problem as they use a very similar database.
i switched to mambo plus (mambo with intergrated database and functions with phpb) now i just have to pray it still works when i upgrade to phpbb3...im expecting a couple of weeks of code writing and im a tad noobish so thats gonna be horible
you've to get the latest release of phpNuke or the phpBB forum update from the phpBB site and upload it to the forum folder inside the phpNuke folder and follow the instructions to upgrade your phpBB forum.