I also recall a while back that some oems, (hp come to mind) had preloaded verisons of a MS works suite that had word 2003 as part of it. that could be why you are seeing a word 2003 key.
and they did have oem and stand alone retail version of it but not any official downloads for it.
as TastesLikeChicken mention, probably best bet if have access to recovery media that has the original word 2003 install files, or if have access to original drive, can look for the hidden msocache folder, that usually has the install files, but I have never tried to re-install from that