If you are wanting to leave the operating system on it but remove everything else, I would uninstall all programs and whatever folders the uninstall leaves behind from the program and then just use something that shreds, rather than just deletes, the files you want to get rid of. I have never used anything to shred a file but they are suppose to make it so that there are not traces of the files and the files cannot be brought back. Spybot has a feature that shreds files but there are many other programs out there that do that too.
Most likely any file removed using any of the shredder programs will still be able to be found by someone in computer forensics or an agency like the CIA or something, but not by the average user.
I would think that reformatting and reinstalling the operating system would be the easiest way to go, that way you don't need to spend all that time uninstalling and deleting stuff. It will also give the new owner of the computer a clean system without a registry that has lots of stuff leftover from the programs you have installed and uninstalled. If you are really concerned about the data surviving a reformat, then use a program that will write 0s to the disk before it formats. Personally, I would just do a regular full (not quick) format.
Also, make sure you give the new owner of the computer the operating system disk and license key.
Edited by Stang777, 31 March 2009 - 08:50 PM.