OK, you know that photo is just too good to not be a fake.  Here is the story, from the National Geographic Site :

"A photograph that has been circulating on the internet showing a shark leaping out of the water to attack a helicopter, is a fake. The composite image, which claims to be National Geographic's "Photo of the Year," was spliced together from a U.S. Air Force photo taken near San Francisco's Golden Gate Bridge and a photo of a shark from South Africa.                                        

The photo of a breaching great white shark was taken by South African photographer Charles Maxwell [see the link to his Web site at the bottom of this page]. The Air Force photo of an HH-60G Pave Hawk helicopter was taken by Lance Cheung. They were spliced together by an unknown person, and reportedly began making the rounds on e-mail in August 2001.

"I'd like to make contact with the person who did this—not to get him or her into trouble, but because it's a lot of fun and it is a good job," Maxwell said. "However, I must make clear that I would not like to see this happen to one of my photographs again. It is wrong to take images from a Web site without permission." Maxwell said he has sold quite a few photographs as a result of the attention the hoax has drawn to his work.