Introducing your new dog to your cat
Next, set up some controlled meetings. Put the dog on lead and walk him into the room where the cat is sitting. Walk him around the room on a loose lead (a tight lead will transmit your anxiety about the situation to the dog). Do not allow the dog to act inappropriately toward the cat (barking, lunging, chasing). A mild correction (“no”) and a request to “sit” should suffice. If the correction is too severe the dog will associate getting into trouble with the cat. Reward calm behavior from the dog using praise and food treats. Give special treats and praise to the cat when the dog is in the room to help create a positive association with the presence of the dog.
The cat may hiss, swat, and growl at the dog. Do not punish her for this or she will associate the dog with the punishment. Repeat these controlled meetings until both animals remain calm and relaxed with each other. Don’t allow the dog to have free run of the house until you are certain the animals are comfortable with one another.
Most dogs and cats can live together peacefully. It is important to remember that dogs are natural predators of cats. For this reason you should never permit the dog to chase the cat or pick her up in his mouth. You may know that the dog has friendly intentions but the cat doesn’t!Source: http://indoorpet.osu.edu/dogs/new_additions_dogs/intro-dog-cat/index.cfm