What are your goals? just lose weight?
As a novice you can gain muscle and burn fat doing just about any type of exercise. Eventually though you'll have to progressively load your muscles to see improvement. This is very difficult to do on a conditioning/aerobic program. You may still be burning fat, but you'll be losing muscle too.
Make sure you're eating enough food too. People like to eat waayy too little when on a new program. If your not eating enough you will not recover and a lot of times your body will hold onto it's fat as a reserve.
My suggestion, drop the p90, pick up a barbell and get as strong as you can. You'll burn fat and look better than you would if you had 'teh ripped core'
I'm not sure what is going on nowadays where guys feel the need to be smaller. I weighed 140 lbs last summer, trust me it's not sexy.