impossible to delete personal details, all logins and passwords can still be retrieved using software.
windows can be installed via usb or memory card slots.
Have a quick read up on the ATA standard "Secure Erase". Even forensic grade software isn't be able to recover data erased in this manner. (Technically data can still be recovered, but it involves dismantling the drive and analysing the platter(s) in an electron microscope...)
However, in this case I think your suggested method of a new hard drive and installing Win/Linux from USB is safer option than messing about with hdparm.