If you format the drives using Windows then I and anyone else with the skills and knowledge will be able to reconstruct your data. You could try deleting your personal data, then defragging, and then writing some junk to the drive. That ought to overwrite your data but the only really safe way is to remove your hard disk and destroy it.
Terry
April 2006
Format the drives and reinstall windows this will put the unit back to basic form.
howtomendit.com for free repair help, information and advice.
Try fixfault.com to fix desktop pcs.