Hi Gustavo. If you want to make still (not carbonated) cider, then you don't need to pastuerizie at all. See the sticky threads at the top of the forum for info on stablizing the cider (stopping the yeast) and then backsweetening.
If you do want to make carbonated cider, then you would pasteurize after the bottles have carbonated. When you pastuerize you kill the yeast, so they won't be able to carbonate your cider.
You might also take a look at www.makinghardcider.com