I have been installing some forum for my property website because I feels that it needed a strong community touch up. phpBB was my initial choice because it is one of the longest open source forum script outside. Unfortunately it is very hard to configure anything in phpBB because you will have to change the code manually, and there is no turning back once the code is edited.
Kimmy introduced MyBB that is used in his community, saying it is easier to install plugins and mods. To my notice, it is real easy. Practically similar to WordPress, you just upload into the plugins forum and activate them. Although I dislike the arrangement of the style in the admin, I must say MyBB is a much easier php script to use.
I choose not to touch phpBB because I have too many scripts to understand at the moment and phpBB will add up to another hard to learn script. Although there is some good debate comparing this 2 forums and both have its pros and cons.