Blogs and forums are two different things, but they don't have to be.
I'm adding a forum to the Rockets blog, where any registered user will be able to post on any topic. Each new blog post will appear on the forum, and any comments added in the forum will be reflected in the blog itself. But the inverse is not true-- any new forum post will not appear on the blog. This allows other users to start discussions and interact with each other without interrupting the blog itself.
The way I do this is to add a new column called "PostType" that can be either "Blog post" or "Forum post". The former will be retrieved by the main page, while the latter is retrieved by the forum page.
I'm also using my new (display-table) function to display the forum posts.