If you didn't have to activate XP, you got the OEM version. Companies like Dell and HP made deals with Microsoft to allow those installs to auto-activate. People who buy XP from the store have to activate it within 30 days of every install and re-activate if they change a certain number of hardware components. Why are you so worried about this? It's completely off topic.
About OEM, I think for Win98 Cds the keys were different, I didnt have to actuivate me XP after installing, only type a products key, but would any key work? Just at the back the number is listed is different?