the main disadvantage with phpBB is that it doesnt support RSS
And also, i tihnk its support for SE friendly URLS is grainy too.
But if you're not concerend about RSS, then phpBB is your choice.
There's also this not-very-well known open source forum script called bbPress, by the creators of WordPress. supports rss and SE friendly URLs. You might also want to try that
Both are great forum system you just have to read the instructions carefully to install its always hard the first time doing something that relates to MySQL but im sure others will back me up in saying this its so easy the second time round.
You can also get portals too called CMS, which basically helps you create your site its really easy too another thing to look into, Simple machines do a free portal and then you can get others like: