I don't think you should be looking at your calories as much as the intensity you are doing your cardio. some research shows that low to mod intensity cardio for a longer duration will tap into your fat stores. ifyou are using a lifefitness machine, it'll have the heartrate scale on the corner. aim for 65% of your mx heart rate.
if you increase your intensity, you will change the ratio of fat used as energy, the more intense, the less likely fat will be the primary source of fuel. of course all research is controversial as certain studies indicate that people who engage in frequent vigorous exericise have less body fat than those who perform only moderate acitivities.
calories should be factored in to coincide with your diet goals at the moment. always rem. to eat enough to compensate for your aerobic and weight training activities.