Dog Afraid of Loud Noises?

[AngelDellaNotte]

Several years ago some kids that lived near me thought it would be funny to throw caps (small fireworks) at my dog. Ever since then she's been terrified of any loud noises. It's been close to two years since the kids did this and her fear still pretty bad. She'll run in the back of the house and curl up under a desk shaking every time she hears a loud noise then proceed to freak out for up to an hour. Does anyone know a good way to retrain her not to be afraid of loud noises?