In the software, forums are typically reserved for groups. Although the software does not allow it out of the box, there is a temporary workaround for implementing a site wide forum until something better comes along.
As the admin, create a Site group. Now you have a group, group members, a forum a gallery etc. Just like any other. Add a task to sql server to add members to this group every XX minutes/hours etc. The time depends on how active your site registrations are and whether or not you implement email verification/account activation.
What ends up happening is that all site members become part of your site group. Be careful to only add those that have not "unjoined" (check the GroupMembers table to see how that's flagged). Don't want to offend people that choose not to be there.
Once you do that, the SQL process will run in the background capturing all of your members once into the site group so they will see new and updated group posts on their homepage.
We run a SQL 2000 back end and can provide the TSQL to do this if there is interest.
Works for now as a solution until a better one is developed, or contributed by other site owners.