Why does my shower have low water pressure and how can I fix it?

I'm a college student and recently moved into a new place. The house has one shower with low pressure. All the other water outlets in the house seem to be normal (sinks, toilet, etc.), but this one shower is really bad. The house is pretty old and there is no real shower head. It's one of those heads that is fastened to a wall and gets it's water through a hose connected to the bath spout. Is it just the head? If I replaced the head, should it be better? or is there something more involved here?