I don't recommend using PHPBB unless you're willing to put time into it. It requires a lot of 'babysitting', you need to update it fairly regularly with security and bug fixes; if you want a low-maintenance site or one you can go off and leave for a few months, PHPBB will stand in your way.
The thing is, unless you sign up for a free forum (like at forumotion), it's not really as simple as a forum 'generator', because any forum you go for will take a lot of time and effort, both when you're promoting it and when it becomes successful (not to mention the tons of bandwidth that the big ones take up). I used to run a forum with about 1000 active members, and my host still complained about the amount of bandwidth I was using (big international host).
More information on what you want would be useful. How many people are you expecting to sign up? How much customisation do you want to have? What 'extras' (virtual/real shop, games, profile customisation etc.) do you want, if any?
