Right. Compatible means you have to know whether your key is for Retail, Upgrade, or OEM.
jkolak: Since you took the "bait", what are the "compatibility" rules? I've never been able to sort that out...
a. So, Retail, Upgrade, OEM "product keys" are not interchangeable?
b. Am I correct in assuming Windows XP Home Edition, Professional, Media Center, and Volume License "product keys" are not interchangeable.
c. What about "product keys" across service pack levels?