The XP Home key IS legitimate. I needed to do a reinstall of XP Home and did not have original media so I first borrowed a full version of XP Home SP2 which failed with a "Key not valid" message. Next I torrented a media-only copy of XP Home SP3 (note this was NOT a crack, just the media itself) which also failed.
1) Why does a legit key on the Windows sticker on the back of the machine fail with different media
2) What are my options for doing a reinstall?