Do you mean a standalone drupal installation, or a
vbDrupal installation?
If you really need the front page stories posted to a forum too, you simply set up the vbulletin comments system to post to the specified 'default' forum for that particular content type. How much of the story is posted to the forum for commenting is specified via the 'teaser', and via the template for the 'post' vbdrupal makes.
I have it set up so blog comments go to one forum, 'news' goes to another, and 'admin stuff' goes to the admin den.