Migrating old hacked database to new hacked database

I'm about to migrate from my old hacked forums to a new one. The new forums have been rehacked from scratch, so there are plenty of new hacks and a few old ones are missing. I would love to be able to import ONLY to fields that are in the new forums. That way I can be sure everything will work. In such a situation, what's the best way to import data? Thanks in advance.