I have 2 dogs with 5 cats, and apart from initial teething problems, have luckily had no problems. The puppy has to learn that it is unacceptable to chase the cat, but they should not be kept apart at all times. With the pup being so young, he should learn pretty quickly that a cats claws mean business!
Both parties should have somewhere to escape the other, and the cat needs safe places to eat, sleep and go to the toilet. I would recommend a strategically placed baby gate (mine is on my kitchen doorway) that the cat can easily get through/under/over, and a dog crate. When the dog gets too boisterous/noisy, and wil not stop after a firm 'NO', in the crate for a time-out. Although the crate should be treated as a safe den, not a punishment. Both my dogs love their crates, and choose to sleep in them though the doors are never closed now.
Btw, Havanese are cute dogs, never seen a pup though so would love to see a pic! As far as breeds go, toy dogs tend to get on best with cats, due to their small size and general social nature, so I do think once your pup has matured a little things will greatly improve.