I have a one year old male daushaund who nips at anyone who comes to the door or talks to us on the street. How do I break him of this correctly?

When he begins to go into this mode give him a stern correction of Ah or No and continue until he is calm.. and check the leash.. Once he is calm.. give him praise...

It sounds like he thinks he is in charge and must handle these people for you. Correcting him for it won't be effective unless he acknowledges you as the leader. The key to most behavior problems is approaching things using the dog's natural instincts. Dogs see all the people and dogs in the household as a pack with each having their own rank in the pack and a top dog. Life is much easier if the 2 legged pack members outrank the 4 legged ones. You can learn to play the role of top dog by reading some books or going to a good obedience class. A good obedience class or book is about you being top dog, not about rewarding standard commands with a treat. Start at Raising Your Dog with the Monks of New Skete For more on being top dog, see Establishing and Keeping Alpha Position, Letting your dog know you are the boss

Neuter him in not already. It should make a big difference, although it is no cure all and must be accompanied by strong leadership. He certainly doesn't sound like a candidate for breeding.

I would rate you as agreed but have to spread around some rep, but you are right.. I forgot to add that you must be in charge and the dog must view you as in charge for corrections to have an effect.