Cross-trainer or treadmill for fat loss?

Ya, as far as the interval thing, high-intensity intervals burn more calories and result in "afterburn" (burning more calories after the session has been completed - for several hours). Studies show that you can burn several times as many calories with much less actual activity (but MUCH more intense).

However, if you are doing demanding bodybuilding-type training sessions (as most fitness models do), you may succumb to "over-training" by also doing HIIT (High Intensity Interval Training). You would also be at high risk of injury. I find that one HIIT session a week, along with 4 brisk walks and a jog per week are a perfect complement to weight training when I'm trying to bring out my 6-pack.

...however, as a sports nutritionist, I have to point out that abs are made in the kitchen - you have to get your diet right!!