Please let me know if you need any more information to help me. I've been thinking about making a switch for a while. I already have the domain purchased, so that part's out of the way. I understand that things such as themes, user scripts, et cetera will likely not be ported.
What matters is that the posts, topics, and users are ported over.
I've got the posts out of our Zetaboards forum by writing a c# HTML to BBCode convertor and screen scraping off the forum, before putting the posts into XML. I'm then using this to to bang the data into phpBB 3.0: