Nuking My Hard Drive

I know how to nuke a PC by using debug and fdisk. What I am looking for is a way to guarantee that there is no way of retrieving any data from a hard drive.

My company is giving away their old computers, but I must wipe everything from the hard drive and reinstall the OS. I also want something that will write ones and zeros on the hard drive to prevent any type of data recovery that the company views as sensitive information.

The operating systems I am working with are 95 and 98SE. Thank you in advance for your help!