I am giving my Inspiron 531 to my son. What is the correct procedure to wiping clean the hard drive?
Reformatting won't wipe the drive; you need a utility like Acronis TrueImage for that.
Unless your son is skilled at digital forensics, however, repartitioning and reformatting should be sufficient. Use the factory WIndows disc to perform a clean install of Windows, and your data will be inaccessible to all but a determined examiner.