Q: please explain how HIIT works? it is the same as weigh training? i have noticed that my heart beats faster during weight lifting is.. is this cardio too?

A: HIIT is a hybrid of weight-training and cardio. You perform an activity (typically running) that's normally considered cardio, but you perform it at such intensity (sprinting) that it elicits largely the same response from your body as does heavy weight-training. If I had to classify HIIT as one or the other, I would group it along with weight-training because of its metabolic demands and the post-training response from your body. Check out http://www.mikesfitness.com/content/nutrition-advice-for-hiit for a bit more on HIIT.

You are correct that your heart will beat faster during weight training and it will actually traing your cardiovascular system to some degree as well (especially if you haven't done much cardio before). But it is not as effective in cardiovascular respect as dedicated cardio training, of course.