As per Tom's answer in the last thread again you need to read up on this subject. You can't get an understanding of indexes by asking questions like this on a forum - or at least not without asking hundreds of questions.
Read up on this and you'll learn that indexes <> primary keys but SQL Server (and most RDMSs) enforce primary keys through unique, non-null indexes. As such, senario 2 is impossible. Also - a primary key does not determine the physical characteristics of a table. The nature of (or lack of) the indexes does.