please take a look here, scroll down.. there is an image of a girl taken with 28mm and 200mm, How can it be if the photographer stands at the same distance from the subject and for both focal ranges the girl occupies the same space in both images.
The photographer DOES NOT stand on the same spot. He moves so that the girl is about the same size on all shots.
Check this out:
Main Page. This is a great site for SLR newbies, it helped me A LOT!: