What we did, and what most people do is to choose a new directory for your forums, convert the data over as a trial run - you can then mess around configuring threads up, altering templates etc. Invite a few select users, to try it, and once you are happy re-convert the forums again.
This way you will have a threads version, with actual data that you can play around in, before making it live.
Your classic version always remains intact - which means that once you move it, don't forget to leave it closed, or remove it, otherwise you will have two forums running
