I always use one of the two following programs for this purpose. Both are excellent:
Low Level Format = Writing Zeros
To completely erase all data on the drive(s), download DBAN
and create a floppy disk to use.
Enter the BIOS setup menu and set the boot order to 'floppy first', then reboot with the DBAN floppy inserted in the drive.
It will completely and securely wipe everything off your hard drive.
: Anytime you use one of these programs, it is a good idea to unhook other hard drives, because some of these programs can wipe more than one drive at a time.