Older Windows OS with a newer OS'es key?

[StrikeRTM]

I don't honestly remember where I heard this or if it's just my imagination, but I think I've red somewhere that if you own a legal activation key for windows, say XP, you could use that same key on the older windows 98. I.e. if you have a newer windows you can use any of the old ones also. So, is this true or not? Could I use a key of Vista Home Premium that I own on a WinXP Pro?

[Newblar]

i dont think so...

[MikeB12]

big fat NOPE...

you can try it.. I have my keys in a .doc and have read the wrong line typing the wrong one before and it fails..

even xp oem and xp retail keys won't interchange.

[Scubar]

Nearly positive it wouldnt work because they would use different alogorythms