Hi DAISY_CHAIN! You're operating on some basic misconceptions, and I think I can help clear them up for you.
No, your calories don't stop "counting." Exercise calories don't make food disappear. It's a common misconception that you can "work off" the food you eat!
Here's what's going on.
You have your BMR (base metabolic rate) that is how many calories you burn at rest, just sitting around doing nothing. This is what your body burns naturally, and is different for most people. That 2,000 calories you see on the side of food's nutrition information label is based on this number for maintenance. Let's use my numbers as an example, since I know what it is. (You can find yours in your calorie differential report here on SP). Mine's 1900.
Assuming you are basically sedentary, you then multiply this number by 1.2 to account for all the other stuff you do; walking to the car, going to the grocery store, walking around at work, etc.
That would make my daily calorie burn without any exercise about 2,280. That means I can eat anywhere from 2000-2300 calories and maintain.
Now, you add on your exercise calories on top of that! If you burn 100 calories, you'd add that on to your daily calorie burn, making it 2,380.
To lose weight, I would then eat LESS than I am burning. To figure out your calorie deficit, you subtract what you're eating from that final number. So, if I were to eat only 1200 calories, I would be creating a HUGE calorie deficit that would be unhealthy for my body. that would be 1,180.
It takes a deficit of 3500 calories to lose a pound, which broken down over a week means you want to create a daily deficit of about 500 calories through diet and exercise to lose weight at the rate of 1 lb per week, a safe amount for my weight and height. I can go up to about 2 lbs, but that creates a larger deficit and means I can't eat as much, and I like food. A lot. :) I don't do that dieting thing.
So, I aim for about 1500-1900 calories a day! I burn anywhere from 200-500 calories a day, depending on what I do. On days when I'm exercising intensely, I NEED my 1900 calories. On days where I'm sedentary, I eat less. I use my range, and you should too! Your range is at least 1200-1550. That's the minimum Sparkrange.
When I first got started, my range was 1900-2200... I was doing tons of bootcamp workouts, and seriously burning a huge amount every day. And yes, I lost. :)
Here's how Sparkpeople does all this: www.sparkpeople.com/resource/calorie_calcu
Does this help?