LOL!! Dogs and cats are not natural enemies. :) It's a funny myth though.
As a professional dog trainer myself, I also recommend obedience training. If your dog is chasing cats and you can't call him off of the cats, then you do not have a good "recall" (ie come command) on your dog. Go to a positive reinforcement trainer and learn how to get your dog to come to you when you call, even when there are strong distractions.
People often look for "magic pills" when trying to deal with dog behavior. Dogs are living beings, and there is no fast fix. A good dog isn't born - he's trained. Take the hours upon hours it will take to train your dog how to be a great and safe companion not only for your but for your community and area cats as well. :)
I have a hub on how to find a good dog obedience trainer. Check it out and go have some fun with your dog!!
http://agilitymach.hubpages.com/hub/The-Top-Ten-Th... trainer. Check it out and go have some training fun with your dog!!