I have a hard drive that contains certain personal data of customers (previously belonged to a small business with which I was involved) - at this point I'm quite low on money so I'm planning to sell it as part of an unwanted PC. But I obviously don't want any unscrupulous types to recover such data from the drive, so I need to use some kind of software to erase and rewrite it, preferably only the unused space (it's got a fresh install of XP on it, just so I can sell to people who don't know shit about computers, and at this point i can't be arsed reinstalling it). Would cipher /w do the job, or do I need something else?