Winter - What I did was install .threads and import from .classic while .c was still up and running. The import for my forum took 9 hours. After some fine-tuning, I opened it up for beta testing to my members concurrently with the .c board running.
Now that I'm happy with it, and the members got to get used to how things work differently... this weekend (assuming traffic will be lightest), I'll need to close down .c (so no posts or new sign-ups are missed during those 9 hours), drop all the tables in .t, then import again. And then, hope for the best!
I REALLY recommend that you involve your members in the process - "test out the new board!" - because most of my visitors were shocked and dare I say, turned off, when they saw the difference. But the more they play with it, now they
LOVE it! (P.S. Shock them less by only using one side column - they really didn't like losing all that real estate they were accustomed to). But like anything else, they
will get used to it!
Hope that helps give you an idea what's in store...