You probably won't have a problem if you'll be getting a puppy. There are a few breeds that have a reputation for being especially aggressive to cats, but even with those breeds, mostly terrier types, there are many exceptions.
When cats are the aggressors, one or two swats on a curious puppy's nose will probably be all it takes to keep the puppy at a safe distance. Any possible future friendship will be on the cat's terms.
Many dogs and cats live together peacefully. They can become best friends. I think Boxers are generally even-tempered dogs.
It depends much more on a dog's age and past experience than on the breed. When you get an adult dog, it's not that simple. If you get a boxer from rescue, the foster care givers will sometimes know if the dog is cat fiendly or not.
For more information on boxers, from people who know the breed, check the forums at
Boxer Friends or
Boxer World. <img src="/images/graemlins/smile.gif" alt="" />
