I have no idea but here is the answer from the mouth of a +++++ Super Server Admin +++++ (hubby of a friend of mine) that is by my side reminding me that is dinner time:
vBulletin should have a converter for this. Invision Power Board has one for their board, and since they are both some of the biggest boards, ask support on VB's Site if they have a converter.
I had to transfer a database for smf awhile ago. It's was about 90mb and I wasn't able to get bigdump to work. I was able to use secureshell to import the whole sql dump file. Sorry I can't remember the exact command but if you google "mysql mass import" I think you'll be able to find more info on it.