If you're worried about passing on personal identity information on the drive such as finances, passwords, etc, I would recommend finding a wiping utility that will replace all the bytes on the drive with 0s. Be aware that formatting a drive doesn't actually clear the hard drive of the data you left behind, it's essentially the same thing as ripping out the table of contents in a book. You lose a record of what pages go where and are for what, but the pages themselves are still there. If you don't care about that, I would just reformat it and install a fresh copy of Windows with the Windows installation utility.