When I needed to send a laptop back to its makers for (non-functional motherboard) repair, we decided to "virginise
" the hard drive
By connecting it as a second drive to the existing Linux box, it came up as hdb and could be mounted, and the Windows directories were available so we took the opportunity to snatch back all the stuff we wanted to salvage. Then a few vicious (and unnecessary) rm commands were used to delete everything, but we went for more..
First fdisk - delete all and made 2 windows partitions, one bootable.
dd if=/dev/zero of=/dev/hda1 bs=512 count=1
The dd command zeros the first 512 bytes of the partition - where the MBR goes.
I *think* it was by leaving out the -Q (quick format) option, that it zeroed the whole volume, but I do remember the process took a while get through the whole 80Gigs because we all got bored and went off to make tea. It was not a forensic overwrite, but the drive ended up functionally "virginal" for all practical purposes. I am not sure what happens if you let Windows to do the job.