I'm buying a new rMBP and giving away my old MBP. I will copy and paste all of my files from my old MBP on to a external hard drive then drag them onto my new rMPB. ---- Question: After copying all of my files onto the external hard drive how do I securely delete every single thing off of my old MacBook Pro (data zero out) before I give it away. (It came with Lion installed), then after nuking it how do I reinstall the OS so I can give it away. Thank you!