This comes from a New York Times technology Q&A column
As a general rule computers need to be upgraded every three to four years. When you get rid of the old computer you can either throw it away, give it away or recycle it. However it leaves your office we have an ethical and legal obligation to be sure there is no personal medical information left on the hard drive. The following addresses these issues.
Taking Extra Steps to a Clean Disk
Q. I was in a store recently to buy a new computer, and asked for software to delete my files permanently before donating my old PC. The sales clerk said I didn’t need to buy the software, as I can do this in Windows by reformatting my drive with the Format command. Will that work?
A. The Format command is often used to prepare a disk for installing (or reinstalling) an operating system, but it does not securely erase all data from the computer. People who know how to dig around and recover data may still be able to mine personal information from your old PC.
Most experts suggest that computer users who need to securely and permanently erase data from a hard drive (the Pentagon, for instance) either physically destroy the drive or use a software utility to thoroughly overwrite all its information. It may take some time, but a good wipe program can repeatedly overwrite your hard drive with random data from 7 to 35 times to erase any personal files lingering on the drive.
There are many commercial software programs for Windows in the $40 to $50 range that can completely erase your hard drive, like WipeDrive (www.whitecanyon.com) and CyberScrub Privacy Suite (www.cyberscrub.com). There are also free options, like Eraser (www.heidi.ie/eraser) and Darik’s Boot and Nuke (dban.sourceforge.net), a small program that can be loaded onto a diskette or recordable CD and used to wipe your drive clean.