The forum software comes as a package, pretty much like any other application. There are both commercial verions, and some free versions. I agree though, the programming behind forums is amazing. As far as people that it takes to run, I think Grinler would tell you that when he first set up BC, he did it all on his own. As the membership has grown, he then added other staff to help run things, but he is still reponsible for everything that happens "behind the scenes".
At a minimum, you need somewhere to host the forum, and some type of forum software. You can either rent server space, or host it off your own Internet Connection (if you have cable or DSL, and do not expect too many users.)
There are quite a few different forum packages... these two are popular and common.http://www.phpbb.com/http://www.yabbforum.com/
That should get you started.