It depends on how fast you want to lose the weight.
If you eat 1500 calories a day, you eat 1500 calories a day, not 1000, no matter what exercise you do.
However, if you burn 500 calories a day more than you eat (exercise plus activity is your burn), then you will lose about a pound a week (a pound being 3500 calories, 500 calorie deficit per day times 7 days).
If you have a deficit of 1000 per day, then you will lose about two pounds a week.
Suppose (and I don't know your #s so I am totally making this up) you burn 2000 calories a day just regular lifestyle (no exercise). If you eat 1500, you will lose about a pound a week (on average). However, if you do exercise each day of the week that burns 500 calories, then you will lose, again on average, 2 pounds per week, because your total burn is 2500 (2000 lifestyle + 500 burned via exercise). But say you burned 2500 and ate 2000 cals per day...then you are back to losing a pound per week because the difference is 500 per day.
"If you drop an egg, you don't say, 'Oh, shoot' and drop the other 11, do you?"
-Source unknown, but obviously brilliant
Reached goal 4/16/2010...but kind of afraid to look these days