i do this as well, not on purpose but just a habit and dont even realise im doing it.. it really sucks :(
what i do is... file all your nails down as short as you can (until you can kick the habit again at least) if you dont have nails you cant pick/scratch!
and you know the vitamin E tablets? you can get them at your local supermarket or chemist (cheapest at the chemist) and cut the top of the tablet and rub the stuff that is inside them on your arms. its not the most pleasant stuff to rub on your body but it is the best thing by far for scars! just rub it on once a day, probs just before you go to bed.
hope that helps x
ive spent my last days thinking about the times i had to spend with you. A day passed, a night faded. im just another, trying to find myself in this crowd. In this place of confusion. A memory that is not wanted. A waste of breath. these tears that fall, not for you, not for anyone anymore.