if your product keys are valid, you can freely and legally download just the software on the disc alone, without a product key, and then use your own key. or, if you can find a demo/trial version of whatever version of office, you can get that, and then egister it with you product key.
yeah why not just download it off the internet and use your valid cd key.
the way i see it,its only like when people make copys of their Os cds for backup purposes just incase the main one gets scratched or something or like yourself it gets lost.