Open Source is the way to go.
And with that I give you:
Eraser
Eraser is an advanced security tool (for Windows), which allows you to completely remove sensitive data from your hard drive by overwriting it several times with carefully selected patterns. Works with Windows 95, 98, ME, NT, 2000, XP and DOS.
Eraser is FREE software and its source code is released under GNU General Public License.
The patterns used for overwriting are based on Peter Gutmann's paper "Secure Deletion of Data from Magnetic and Solid-State Memory" and they are selected to effectively remove magnetic remnants from the hard drive.
Other methods include the one defined in the National Industrial Security Program Operating Manual of the US Department of Defence and overwriting with pseudorandom data. You can also define your own overwriting methods.
Home Page:
hxxp://www.heidi.ie/eraser/
Download:
hxxp://prdownloads.sourceforge.net/eraser/Eraser57Setup.zip
Just create a nuke boot disk. And let baby take care of it. I let it run for at least a week.
How do I Erase my entire hard drive(s) on my PC?
Eraser uses the 'Darik's Boot and Nuke' disk option to erase all your hard drives.
To use this option:
1. Place a floppy (or CD) in your a: drive.
2. Click on the Start button and then choose Programs->Eraser->Create Boot Nuke Disk.
3. Ensure 'Writing on Floppy' is ticked. Tick 'Formatting' if your floppy needs to be formatted.
4. Click OK. Result: Your Boot Nuke Disk has now been created.
5. Boot up your PC with the floppy still remaining in your a: drive.
Remember: If you wish to erase the Hard Disk of another PC, then bring this Floppy to the PC, insert it into the a: drive and Boot it up.
Result: All drives will now be erased (including the Operating System)
IMPORTANT: USE WITH EXTREME CAUTION
For a summary:
'Darik's Boot and Nuke' ("DBAN") is a self-contained boot floppy that securely wipes the hard disks of most computers. DBAN will automatically and completely delete the contents of any hard disk that it can detect, which makes it an appropriate utility for bulk or emergency data destruction.'
More Information About It Here:
hxxp://sourceforge.net/projects/dban/