On the menu bar, click on what looks like a colored bar graph (between the target and the thumb print). There are a variety of percentages depending on your goals, but 20%fat, 30% protein, 50% carbs is a good place to start. Then adjust from there depending on your goals.
It does seem like it would be nice if Diet Power would be able to match NQ to your own preferred target ratios. I suspect these ratios are something of a fad but they seem to have stuck around for quite a while now and I am sure lots of people would like to be able to get NQ to only give them an A if stuck to thier diet (which might be eat as much fat and protein as you like so long as you dont eat more than 20/40/60 net carbs...)
Anyway I've done South Beach and lost weight but it all came back. Felt good for awhile but got boring. Just following Diet Power to deal with simple mass balance (calories in minus calories out = weight gain/loss) has been most successful diet I've tried.