I agree with wishes 1000%. I lost 112 pounds in 26 weeks. It was not easy and you need to stay focused but I did not do anything crazy to achieve this, I just started eating healthier and getting some exercise. I cut all soda, junk food and late night snacks out, watched portion size, drank lots of water, and started eating lots of fruits and veggies. I was not trying to lose it that fast it just happened that way. I bought a couple of nutritional books and visited a registered dietitian in an effort to learn and make sure I was doing it right. I think intentionally limiting yourself to 1 or 2 pounds a week is crazy. If you are eating well and exercising and happen to be losing faster than most others then keep up the good work and go for it.
Shotgun, having said all that I also want to stress that you should not try to win this bet at the expence of your health, please do it safely, try to learn about foods and nutrition. If you do lose 100 pounds I can almost guarantee that being 100 pounds lighter will be a much sweeter victory than the $200.