Drupal 7 default Forum styling for custom content type? Im using Drupal 7's forum module. Its working great but I need to also make a custom content type a forum. 

I can allow comments on this custom content type, but can I make it have the same styling as the default forum content type? 

UPDATE - The reason I need this is there are 2 user roles. Only registered users can see forums at all. Users with a special role can see private forums aswell.
By 'have the same styling', I'm assuming what you mean is have the same structure and functionality as the Drupal core forum (i.e. threaded discussions). You can always modify the content template to match the same layout and css styling of the core forum module but just enabling comments won't give you the same functionality as forums. The forums module uses comments but adds another layer of management on top which is where you get your threaded discussion. A comments-only content-type would also not integrate with forum add-ons like Advanced Forum. 

You're best option is to create two distinct forums and then (as @frazras notes) use Forum Access module to control access based on your criteria.