webserver you ask? http://apache.org
i'll highlight some points about these boards
YaBB: easy to setup, easy to use but doesn't look the cutest and you can not have polls on it
phpBB: easy to setup, requires MySQL and is a pretty good all around board. it looks pretty nice and does pretty much everything you need in a forum
ikonboard: very flexable as to what you can do. very customizable and LOTS of options
vBulletin: most customizable of all and has the most stuff but it costs you money
although i think PHP is great, i actually recommend ikonboard over all the other ones listed. ikonboard can do so many things that it is incredible, the template is VERY easy to change and it has all the bells and whistles you could ever need (unless people are posting code which is where vBulletin comes in handy)
