I usually warm up before lifting weights. I do some 3 sets of jumping jacks, A LOT of stretching on Squat day. Stretching all your major body parts and jumping jacks works wonders! It gets you going. Then I hit the weights and at the end 20 minutes of non-stop running at 6 mph.
It is recommended to do cardio after lifting weights. I would push hard on the weights then finish it off with the cardio.