Advice on Heart Rate Monitor/Calorie Counter

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Hey Everyone!

I am looking to purchase my first heart rate monitor. I am a bit confused though on what I should be looking for. I know some count calories/heart rate for jogging/walking. But I rarely EVER jog or walk. Most of my workouts consist of Jillian Micahel's DVDs (actually that's all I do. She has helped me go from a size 10 to a size 6.) Do I need a HRM that counts aerobic steps, or would a traditional HRM do the job?

Also, for those that have the body bug, is it worth the cost?