I owned a rather large community since 97 and had some really crappy forum softwares, but until 2003 where I used InvisionBoard, and is pretty good, though not free these days. The software is great and modding it is fun. Others? Well, not too found of, though vBulletin is okay, just not as powerful as Invisions', my opinion, though some may disagree. Know a lot about of forums: installing, skinning, you name it, PHP & MYSQL expert here, though my community got devoured by dust bunnies end of last year, due to my lack of appearance (busy with life and hardships) and the lack of the admins help that are there, though don't know why they can't just take over, so not up-to-update as I use to be...
NOTE: Make sure your site supports php & SQL scripting, otherwise you might not get it too work, some server hosters don't support it. You can get a free database organizer here (phpMyAdmin):
http://www.phpmyadmin.net/home_page/index.php