What is the best program I can get to clean the information off my computer?

I have a couple of desktop and laptop computers I would like to clear out any personal information they might have and donate them to a school in my area. I want to make sure that all my photos banking and all my personal information is gone first. I bought a program called Drive Scrubber and on the box it says it works with 32 and 64 bit. When I went to install the disc I got a message saying it is not compatible with 64 bit. I have Vista on these two computers I tried this out on. Any suggestions on another program that I can buy that is compatible with Vista 64 bit etc? Whatever works I will be glad to buy it so I can clean up these computers and give them to a school or a person who would like a computer and cannot afford to spend alot on a new one. Why would Drive Scrubber say it works with 32 and 64 bit and Vista,XP ,2000 and Windows 7 but it will not work on my Vista 64 bit computer.