I recently got a good deal on a MBP and had perviously purchased a 20 in imac ICD. I dont use the imac any more and am tyring to sell it before it gets an update. What do I need to do to prepare it for sale. I can reinstall tiger and to an earse and install but I read some where that you can do an earse from tiger with 7 x overwirte. How do you do this?