I used phpBB for the forums here. It's free, and works pretty well. You need a host with some flavor of linux running Apache, PHP and MySQL. I think there's a windows equivalent, but I have zero experience with it.
You can grab phpbb from
www.phpbb.com. To handle upgrades and mods you'll need a little bit of programming experience, but to run a vanilla flavored forum it's just a matter of uploading the files and pointing your browser to the forums page. There's tons of help on phpbb's forum.
The doink forums are the latest version of phpBB, with the Attachment Mod (for attaching files), and the phpVB2 theme (makes the board look more like vBullitin.. but I had to mod it to work with the attachment mod ;x ). I also modded the themes to put the Doink logo in the corner... normally it's the pbpBB logo, but there's instructions on how to do that on phpBB's site.
If you have any problems, hit up my ICQ or AIM, but if I'm at work, I may be a little spotty since I'll be multitasking to help ya.