Okay well the upgrade to VB4.x went better than I had expected.
I had expected the forums to fail horribly and the entire DB to go up in flames, possibly burning down the data-center where our server is located and causing all sorts of havoc. Instead there were just a couple of php errors to take care of and that was pretty much it.
Also there is a shitload more setup that needs to be done to get everything running 100% including loading a new forum style, figuring out how the **** the CMS works, etc.
So all in all the upgrade went off without a hitch but now comes the fun part of actually getting everything set up and more or less back to normal.
For now the forums work as they should at least