I know exactly what you mean. I'll eat one off track meal and go over my normal 1200 cals and will gain like a pound. I know I didn't eat enough to gain a pound, but it happens. I guess it has to do with water retention, sodium intake, etc etc. Whatever, it doesn't always make sense, but it happens. I try not to focus on the scale and then before you know it, you're two pounds down easily. I don't know the exact science, but we lose weight eventually right? I do notice that no matter how low my calorie intake is, if I workout, I most always lose 'something' or NOT gain anything. That's really cool you got the zumba DVDs, keep that up, you'll do just fine
Like other posters, I LOVE zumba, I do it about 4 times a week. It's too much fun to be considered a workout..