I've used phpBB in the past, and currently use e107 and its built-in forum. Unless you really want to manage the box yourself, I'd recommend going with a hosting service that covers all the bases. I use modwest.com, and they're fantastic. (I think they're dual OC-192 homed.) Stick with PHP, MySQL, and Apache unless you have a dying need to do something else.
If you want to go beyond just a forum, I'd recommend going over to cmsmatrix.org and comparing the features you want. I'm happy with e107, although it really depends upon your target. Don't bother learning PHP yourself unless you really, really need/want to. Just get a good CMS, install it, regularly back it up (I recommend a script that creates a tarball of the important files and an sql dump at least once a week) and make sure you keep up with major security fixes. (I've had forums hacked twice, but no problems since moving to e107.)
It *will* be a bit overwhelming at first to work with a CMS... especially if you're trying to theme or customize it. Running a straightforward forum is usually really, really easy... harder to keep the members in line and attract new traffic.
Finaly word of caution: You *must* be really dedicated to whatever the subject of your forum is. It takes *serious* commitment to keep the whole thing going, keeping up the interest level, keeping up the discussion level, and carrying through on simple maintenance. The forum will die if you (or somebody) isn't willing to be an evangelist and keep up the excitement level.
This forum (Beyond3D) has dozens (if not hundreds) of people who post interesting content and generate the draw for the rest of the people who are here just to read and browse around the edges. It takes some serious time and energy (and sometimes luck/timing) to draw in those people that make the forum live and breathe.
Good luck with it.
