http://www.dban.org/The best out there.... Makes a boot-able floppy, cd, dvd, or USB flash card..
Just type in AUTONUKE and it go over the entire drive backwards and forwards 3 times....
Hard Drive manufacturers make some tools that will let you do a low level format which is really all you need....
What you are doing is actually zero-ing out the hard drive, in essence.. Hard Drives store binary code(ones and zeroes).
Sorry if you already know this stuff...
But yeah, I'd recommend DBAN... And if you have problems making a boot-able CD, Floppy, or USB memory stick, they
have a detailed tutorial on how to do this.. I think they actually have an ISO that will transfer directly to a CD/DVD..