getting rid of old computers

I am a small business owner that has very sensitive data on my computers.

When I dispose of these computers, what is the safest way to do so and ensure that no data is "stolen" from them?

I would like to sell them, or use them in a different way, but I'm paranoid and continue to store them in my home.

Is it something that I can do myself, or pay someone to do it? If paying someone is the best way, how much would it cost roughly?

Thanks!

 

You can wipe the drives securely yourself, for free. It will only take some time. Most hard drive makers have a tool for securely wiping drives built-in to their diagnostic tools. These tools are free downloads from the manufacturer's web site. You'd create the bootable CD as per their instructions, boot to it, and then use the "Write zeroes to disk" feature. You can also use Dark's Boot-n-Nuke or Active KillDisk. Either one is a free program and the download is used to create a bootable CD or floppy. Boot to it and follow the on-screen prompts. Just remember that when using a drive wiping tool, anything on the drive will be GONE FOREVER!! You or anyone else will be unable to recover any data from the drive so be sure that anything you might need/want someday is saved in advance. Alternatively, you could remove the hard drives and keep 'em.
:-D

 

This is some thing you are able to do yourself (for free)
If you download Killdisk and burn it to a CD/DVD then boot the PC you want to clean with the disk in the drive it will give you a menu of the disks in the PC and you can remove all data (irretrievably) but if you sell them on they will have no OS unless you sell the disks with them.

http://majorgeeks.com/Active_KillDisk_d4791.html

 

If i have a OS restore CD from Dell for a particular computer, can it be installed on a different computer to get the OS installed?

As you can see I am fairly ignorant on the subject. Thanks