This is from my hub on the issue:
How can I make my dog less jealous?
1. Walk your dog: I know I emphasize this a lot but it really is the answer to a lot of behavioral problems like digging and excessive barking. If your dog is jealous, but tired, she will be less likely to display jealousy. It is good for your health too!
2. Make her more submissive by reinforcing your role as leader of the pack. If your dog is displaying jealousy because of feeling she is in charge, this will help.
3. Use counterconditioning techniques to make your dog associate the new object (new puppy, new baby) with a pleasant experience. You can read the article about fireworks to see a discussion of conditioning.
4. Have your male dog neutered if he is displaying aggression while jealous. Neutering is not always a solution for aggression but this is a possible solution you might want to try.
5. If none of the other solutions work, have a good physical exam conducted to rule out a medical cause.
6. If everything else is normal, and the dog is still displaying jealousy, consult a behaviorist.
Since you do not give any details on your dog, (sex, age, background, etc) there is not a lot else I can do. If you try these solutions and are still having problems you can leave a message on my hub on jealousy.