If after 1-2 min you tend to be normal but are still not getting second interviews/offers, I really don't think it's due to your nerves that you are striking out. Unless the job you are applying for requires nerves of steel or lots of posturing during client meetings, most interviewers will understand and accept 1-2 mins of nerves. You may want to relook the content of your answers.

But worse comes to worst, just apologise for the tremble in your voice and blame air-conditioning in the waiting area. =p