Create a new folder in your File Manager called "forum" and using Fantastico, install the forum to that directory file.
SMF forums are the easiest to play around with, plus you get loads of mods so you can have really good plugins. Have a look
@ Ectomorph, I don't think it looks like a vB style.. Id probably say phpBB and myBB, both easy to install but myBB would be closest to vB (feature wise). Good luck!
MyBB is an easy install as while. If your looking for something like that. You can install mods and it will be just like having vBulletin.