almaznz: if you purchased the OEM for a single machine, then you can install it on that machine with no worries, if the hard drive died and then you replaced said harddrive and reinstalled then you need to ring to get the activation going again. it is only if you purchased the OEM wanting to put it onto two seperate machines at the same time where you may run into issues. but even then i don't think microsoft will be sending in the heavy guns for that
Don't quote me on this but I suspect if you tried to install the OEM or any release on more than one machine then the second time you tried to activate it, it might not let you? Or maybe it's a sort of VLK version?
There seem to be several flavours of OEM licences. We often buy PC's in bulk and each has an OEM sticker on them with a different serial number. But on closer examination the serial number on the box is not what is actually installed with Windows and from the same vendor, we find the same serial number on all of the machines we bought.
Then when I want to just buy a full copy or upgrade copy of Windows for a existing hardware I just use a VLK which has a maximum number of activations attached to it (I think ours is about 100 x the number of staff we have) and just tell our LAR to bill us for the additional copies purchased.