Well...pretty much every forum name with webmaster in it is taken. Don't do a "talk" something, those are pretty much gone. Really, if you want to have a large forum, try an idea no one has thought of. That's the best way. There are a lot of webmaster forums already.

And forum software...go with vBulletin. Others make you look cheap. You want members to think that you really put time into it(which you would have if you paid for vB and the yearly updates)

Of course, I wish I had extra money lying around for a vB license...