When introducing a dog to a cat, the question is really one of proper dog training. Dogs usually want to chase and play with cats, and cats are usually afraid and defensive. After all, the cat has a lot more to lose if the relationship gets nasty. Once the cat is confident that the dog does not pose a threat, then the opportunity opens for a wonderful friendship to blossom.
Keeping the dog on a leash at all times when the introduction is to start, if the dog sees the cat keep them from barking, growling or lunging toward the cat. Reward the dog with treats or a favorite toy if he obeys. (NOT a squeak toy, this will frighten the cat.) Don’t yell or scream at the dog for not obeying, this behavior will only scare the cat and the cat will associate your yelling and fear with seeing the dog. NEVER allow the dog to chase the cat, if this is allowed to happen, just one time, getting the two to accept each other will almost be impossible. Keep the dog on leash at all times until he sees the cat and does not get aggressive. The dog generally just wants to play and chase the cat. The cat on the other hand associates this behavior with aggression and fear, and will want to get away.
This needs to be done slowly, once the cat is not afraid of the dog and the dog shows no concern with the cat in the same room you will have peace and harmony. A happy cat and dog. They will become long lasting friends. You may even find them sleeping together.