Many dogs have inadvertently learned incorrect behaviour from their owners and require to be educated in how to behave correctly. It would be very unusual for a dog to be simply "bad" or "untrainable", in the vast majority of cases the dog has simply learned bad behaviour - or not learned "good" behaviour!
The first step is to remain calm and in control, shouting, smacking and screaming are not as effective as consistent positive training (i.e. rewarding the dog for good behaviour - with treats initially and then just with attention, cuddles etc - and ignoring them when they behave inappropriately).
Secondly make sure the dog realises that you are the "pack leader" and not the other way around, many owners try to spoil their dogs in the vain hope of an easy life - this is far from the case, once your dog realises that it can get the attention/treats/rewards it desires by repeating patterns of (bad) behaviour, essentially the dog will be training you! This is why many people have barking problems with their dogs. Most dogs dont realise whether barking is a good thing or a bad thing. Sometimes when the dog barks, it is ignored. Other times, the dog is praised (warding off possible intruders). And yet other times, the dog is shouted at (owner has a headache/is tired/is on the telephone etc). People are consistently inconsistent, especially when it comes to their pets!
When it comes to housetraining, remember that your dog is an instinctively clean animal. If the dog can avoid it, it would rather not soil itself or her usual eating and sleeping area. All the dog needs is positive encouragement when it eliminates in correct places.
A popular, modern method for dog training and obedience is "Clicker training", this is a slang term used to describe a way of training dogs that has become increasingly popular in the last decade due to its gentle and effective methods. The scientific term for it is operant conditioning. Simply put simply put, an dog tends to repeat an action that has a positive consequence and tends not to repeat one that has a negative consequence. The problem with other types of conditioning is that it is difficult to reinforce good behaviour at a distance, the clicker allows you to mark with great precision the good behaviour for which the dog is being reinforced, even if it the dog is some distance from you.
The clicker is a simple cheap and effective device, basically it's just a metal strip encased in a plastic box that when pressed makes a unique sharp clicking noise that the dog can distinguish easily from background noises. If you are having any problems training your dog this should be the first product on your shopping list.