When its time for a national forum to become several regional forums? How to plan?

[Make Money?]

So I have an idea for a forum.

If and when it takes off, it would need to have a general discussion forum area, and then have regional location discussion areas..

This must be quite common, I suppose if for example you had a sports forum, you could have a main area then section it off into lots of little sub forums. I suppose its possible to duplicate sub forums?

Websites like Craigslist have local versions of the same site...

Can anyone give me some pointers? Some threads here to look at? Some VB sites that do this?

Any coders out there have this sort of thing in your portfolios already?

Thanks in advance,