If you know someone with a welder get him to strike an arc on the case, 50 volts at about 300 amps will create enough of an electromagnetic field to fry any HDD
Hook up jumper cables to your car battery and touch both ends to the drive, that will (0) the thing out . No dont do that really, if it blew up or you got hurt it would be my fault!
Reformatting only erases the directory. Most data recovery software can bring it right back.
There's a free program which will wipe a HDD completely by overwriting the entire drive. You can get it at http://www.heidi.ie/eraser