As a caveat if you are going to ubbthreads.
The importer script only works with a functioning classic board. It does not import a classic export file into threads.
At least as far as I know from when i upgraded.
So that means if you don't have your classic board running even the old version(which I believe will import to threads). You may be starting with a completely clean slate no posts from the prior board.
Of course whatever the problem is you have now may not impact the conversion(import).