Change in Demand vs. Change in Quantity Demanded:
In economics, these two changes both are based off of our economic wants and prices that the consumer is willing to pay for a certain number of goods. The Law of Diminishing Marginal Utility makes the demand curve slope downwards due to the fact that the more a product is consumed, the less utility is gained. A change in demand results in a curve shift, either moving to the left or right. The determinates involved in changes in demand are:

1. Changes in consumer preference
2. Changes in population
3. Changes in income
a. Inferior goods, as income rises we buy less, demand goes down
b. Normal goods, as income rises, demand goes up
4. Changes in related goods prices
a. Substitutes, as the price of it's substitute rises, the demand for that good increases
b. Complements, as the price of it's complement rises, the demand for that good decreases
5. Changes in price expectations

Changes in quantity demanded do NOT move the entire curve, but rather a movement along the curve. Quantity demanded is only affected by changes in price of that good demanded. When the price rises, the demand for that good decreases. When the price decreases, the demand for that good increases. This can be seen through the downward sloping line of the demand curve, as seen below:
*Watch the demand curve develop:
external image Demand_Curve-Plot-ani.gif

Question:
If the the price of a complement good rises, what happens to the demand curve?

Links:
Quantity demanded vs. Changes in Quantity Demanded: This link shows the differences between changes in Quantity Demanded vs. Changes in Quantity Demanded
Shows the Basics- this is a very basic site that provides quick explannations of the differences
Wikipedia's definition


Answer: The demand curve shifts to the left. The demand goes down.