if you watch the show "good dog U" on animal planet, this morning they did a whole episode on barking. at the beginning they talked about a dog that went crazy when the doorbell rang. here's what the host did to help her out:

you have to stay with your dog, a few feet from the door and have someone else help you do it. your friend should be outside, and ringing the doorbell. meanwhile, your going to be inside, with a leash on your dog and you should be crouched down at the same height as your dog. when your friend rings the doorbell, and your dog starts barking, pull gently on the leash and say, "no". repeat and each day, move closer to the door.

hope this helps..good luck