It is a nerve racking thing.. an interview for a job you really want.  Anyone that says it isn't, I would question how much they want it!  There are some really obvious buying signals here, a prospective employer might give away...however also a few others that might make your self doubt turn into positive thoughts post that interview...  I think that being shown around the office and environment, promoting the company  and discussing the next stage in the process are great signals you have nailed the interview!