Dogs and agression

Question
I am getting a yorkie puppy but my oldest dog which is a black lab gets really jealous when I give to much attention to my other dog who is a boxer mix. She will growl and if the boxer mix trys licking her she snaps at her if I am petting the black lab and the boxer mix tries to interfere. So I am afraid that my black lab is going to attack the yorkie because I will be giving the yorkie a lot of attention and he will be very small and easily hurt if the black lab tries to snap at him.

Answer
Spay the Lab if not already.  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 http://www.dogsbestfriend.com/ For more on being top dog, see http://www.dogbreedinfo.com./topdogrules.htm

I hope you are planning a male Yorkie.  A female is much more likely to accept a male than another female.  You are already having trouble with 2 females.  a third one could be a problem.