If you are thinking about adding a forum to your WP blog, heres some helpful information and some tips.
There are several options here, two main ones:
Integrating External Forum Software:
There are plugins and documentation to use Simple Machines Forum (SMF) and combine your Wordpress userbase and make the two work together, there are at least two plugins available to simplify this procedure. The documentation is extensive and a bit complex.
Integrating Internal Forum Software:
These are more light weight, but provide easy setup and configuration, as they are simply Wordpress plugins..
There are at least two available:
RS-Discuss
XDForum
Good luck with your envdeavors and to see XDForum in action, or
to read more, visit
Incorporating a Forum into Your Wordpress Blog | Blogger Chat