Making a backup copy of the installation CD and running a copy on two machines aren't the same thing though - you can copy the disc for personal use but most software is only licensed for use on one machine at a time. Not that most people are bothered about it though, it only really matters if you're running a business as you can then get busted by people like the BSA if you don't follow the licences to the letter. As a home user it's largely irrelevant, maybe a moral issue for some people with newer stuff like OS X but it doesn't really make any difference for abandonware as you can't pay Apple for additional licences any more anyway.