Erm... yea. Not much to follow up on.
Vbulliten is quite possible the best forum software out there. But as Daedaelus said its not cheap at all. But you get what you pay for. Its much faster than other forum software and has the best customer support. You can pirate a copy, of course but you wont get the coustomer support that you would since you will have no member ID so you will be in the dark about many things.
I have also used phpBB (its the one I use for my site in my sig). Its the best free solution out there. My only main gripe is that a lot of the things are manual with it. For example if you want to like change some of the forum's text or add something of your own you are gonna have to go and change muliple files because of the way they have things skinned. Its also a tad slower than other forums.
But those are for if you have php and a sql database installed on your server. I think vBulliten has a cgi version also but I'm not sure.
If you have a good host there should be already a forum ready for your disposal. My host had xmb already there for me but I didnt choose it because I wasnt that familiar with it.
And yea, as Daedaelus said it would be nice to have some php and mySQL knowledge when installing and running one of them. I had to go into the database directly to fix a few problems a couple of times.