it is important to warm up before any exercise - whether weight training, running, yoga, etc. as for the comment as to doing weights first and then cardio because of fat burning impacts - it sounds a bit washy for me. every body is different.

If you are doing weights and cardio within one session do a 10 min warm up and then do your weights. don't warm up with weights - do some form of cardio gently to get your blood pumping and your muscles warm.

if you go gut busters with a cardio workout before strength training, you are going to be sacrificing form on your weights - which means you won't do the movement correctly and could be more susceptable to injury. Do the weights first and then do the cardio afterwards.

i agree with lockitup. the concept of burning calories, carbs or fat doesn't really matter. in the end you are burning excess calories in whatever form it takes.