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I hope I understand your question. By default the setting for comments (wich is linked to the forum) are thread. For a forum most people want to use flat.
For that you don't need to edit any templates. Go to admin/site preferences/general settings. There you will find this: "Default Comment Display Mode". Set this to "flat". After that change the same option in your personal settings as this won't affect users who have already registered.
I hope this is the answer you were looking for.