Toby,
I am afraid there is no easy way to remove the group and forum headings… you can try reading the guide on hooks, but not sure you can even do it there, though V3 may make that possible… of course, by hacking the core code, this would be possible… (look in sf-page.php for page rendering where it draws the group and forum headings)
you certainly cannot put the new topic icon there because it is directly related to a specific forum that you want the new topic to reside in… If you have a mixture or groups/forums on the page, how would it know where to stick the new topic? (without redesigning how the new topic functionality works)…
I am not sure that I follow why you want to do this either…
Is this for display purposes? There is a template tag for only displaying the most recent posts that would look similar to what you have shown (minus the add topic button)… cant remember the name but something like sf_expanded_posts()… you can find it in sf-tags.php… However, it is template tag code, so it would reside on a non forum page…