Ruben pretty much nailed it. While you can use the config file from your current version, there are just a few things that have a database counterpart to the config file. Such as portal settings, the layout is stored in the config file, but the actual settings for each portal box is stored in the database.
So, you can use the old config file, but if you notice any oddities, you'll want to go into the control panel and redit the area in question so the database is updated to match.
