Originally Posted by DJ-CHRIS
Typically 3 activations per key
Let's clarify this, before we encourage a member of CF to engage in illegal use of software. Three activations may be the total available to you, before you may be required to contact Microsoft. This also means you can only activate this key on ONE pc at a time (legally on only the original pc it came on - particularly if it is OEM) ... NOT three pc's simultaneously.
So to answer the original question posted. No ... you cannot legally use one key on multiple computers. And odds are ... if what you have is indeed a Recovery CD, you shouldn't be able to load it on any other pc than the one it came on.