Sounds like he wants some kind of dynamic forum hosting solution.. ie: you sign up as 'xyz' and you create a 'xyz.some-free-forum-host.org' subdomain with a forum ready to go.
If I'm right, there's noway in hell I'm going to write a post here on how to achieve it.. far too complicated for the OP (no offence) and a summary will lead to wanting to be spoon fed.
Regards,
Ian