There is no need to take any risk of leaking information.
1. Your question has been asked before.
2. It's been discussed.
There is no tool to clean off your private information. For example read http://forums.cnet.com/5208-6132_102-0.html?threadID=119247
It's a donation so a clean hard drive makes it ready for them to install their OS.
The suggestions are to use DBAN from http://www.dban.org/
I want to donate several machines I do not use anymore, but I want to remove the owner (a business, all machines were networked!) Any help on how to do that?