Don't know what you lot are complaining about, my last interview went for 8 hours, first was a panel interview with 5 people, then another 4 one on one sessions
Felt rather good to be offered the job, only to turn it down.
Back to the OP - one way I deal with the nerves during interviews is to remember that not only are they assessing you for suitability for the role, but you are also assessing them to see if you would want to work there. Be inquisitive, ask about their operation, put the spotlight back on them, make them ask some questions. Deep down people love talking about themselves, this makes them feel good, and they will associate that good feeling with you.
It also demonstrates that you have interest and ambition.
The other thing I would recommend is practice answering this question - "why should I employ you instead of the other guy sitting outside?", this will help you focus on your salesmanship. Essentially all that an interview is. You are trying to sell your services, so sell them.