You are talking about leaving it install into a PC, correct? Not taking it out and putting it into a HD NAS unit?
You can choose to share a directory on that HD, enable file sharing, and make sure that the username/password combo that you use to access that share is on every machine.
You will then need to find backup software to install onto those other machines, and make certain that it supports backing up to a network drive. That's usually an advanced feature and costs more.