Okay just for you, and this is from memory.

Logout of everything, and close classic to public.

You will use a special path to run the importer.
You get a log in screen for the importer.
And its there you will enter your admin details.

So your logged in now to the importer of threads

You wont be able to log in to the New Threads until the import
has completed, as the importer will create the tables and such.

At the end when its all done, you will get a message saying
you can now log into your forums.

THREADS

You have to be logged in as an admin to run the importer iirc.

classic it doens't matter if you're logged in or not.

Thanks folks