The first foster kitten I brought home, one of the dogs, Fudge, almost killed it. There still seems to be a problem with very young kittens, but 3+ month old kittens, he loves to chase, but so far no more incidents.
As long as the dog is not truly trying to EAT the cat, it could just be a very very heightened interest and attraction to something so new and different. I simply started allowing Fudge in the room with a cat, and any time he would ignore the cat's warning or was getting to interested, he was corrected and taken away from the cat, and we'd start over. His reward was being able to interact with the cat, punishment was being taken away. I would never allow him alone with a cat still, but he and cats can be in the same room now with supervision with virtually no worry at all.
Also, do you have high places the cat can retreat to?