If the genuine copy you have now is being put out of use in one machine and installed in another, it should activate as a legitimate system. You can only use it in one machine at any time but if you buy the upgrade package to use on another system, you will be within the rules.
Thanks for the reply. Yes, I believe we are talking the same thing. I want to use the copy of Win7x64 (OEM) that I have now on other machines as I build them. But I don't want to have to keep buying new OEM copies of Win7 as I do it. I was trying to find the least expensive way of converting my existing copy of Win7 (OEM) to a full license w/o purchasing yet another $200 retail Win7 pkg. I saw the retail upgrade offered at $149. Is that what the upgrade is intended to be used for?
I am aware that I will have to wipe it from PC (A) before I install/activate it on PC (B).