Does anyone know witch free forum software is best, and how do I begin installing it on my site.
Tnx
I like most others would recommend phpBB2. This forum is a phpBB2 forum. It is free to use. Other free forums include the Simple Machine Forums (demo here). The most popular paid forum is probably Invision Power Board (demo here). Invision Power Board is not allowed to be installed on FriHost. If you would like phpBB installed for you then read this topic or you can read this to try and install it yourself.
There is, of course, an example forum hosted at that site too.
It doesn't have a lot of flashy graphics and crazy feaures. Instead it has super-clean code which is easy to understand - and modify to your own liking (if that's your deal). The HTML output is also hyper-clean (which turns it into probably the fastest board around in that regard). And there's plenty of "mods" for adding the more site-specific features like polls etc.
And yes, it's free and open source.
I've used it before, and if I'd ever want to add a forum to some site again (and the server supported PHP), I'd go for punBB once more
EDIT: "mods" for punBB right now are done "simply" by directly modifying the source. Takes some work when you upgrade to a new version. But I just noticed (haven't used it or been at the site for a year or so) that the next version will have an extension ("plugin") system which allows you to install and uninstall additional features. Just about the last thing it was missing to make it just... perfect