1) Yes this is possible, you need to set-up the forum permissions correctly for each group. You can read about that here:
http://www.vbulletin.com/docs/html/u...anaging_forum_
2) To delete the post click on the edit button and check the 'delete post' box on the editpost page. If the post is the first on in the thread, the entire thread is deleted.
Currently there is no option to show an 'attachment was removed from this post' message. But it would be rather easy to hack in.