Just remember that there's no such thing as targeting specific muscles to reduce the size of the fat nearby. Ab work will definitely tone the muscles of your tummy, but the fat can only be reduced by reducing your overall caloric intake. Read more in one of the sticky posts of this forum:
http://www.3fatchicks.com/forum/exer...ise-myths.html
Sit-ups are actually not the best exercise for the stomach since it puts an unnatural curve in the spine (which your body is positioned in all day long if you're sitting at a desk/in front of a computer, etc). Better are planks- basically like holding the start of a push-up except you're on your forearms instead of hands. Side planks (turning to the side so that only one arm and leg are on the ground) and planks with only one leg at a time are also good. It looks like a number of the excercises in the video that
saef posted include planks and work along the principle of ensuring spinal safety and alignment during ab work.
Happy fitness