I see the COA license for windows on pricewatch which is serial number only without the CD. I don't see anything like this on Ebay or any of the big trading forums.
A COA (Certificate of Authorization) is a product key for installing an OEM version of software. For instance, if you are building 5 PCs, you can buy one OEM CD of XP Home/Pro and 5 COAs and use the same CD for all 5 PCs. Pretty good deal, you pay $91 for the first OEM Home XP @ Newegg and around $50 for each subsequent license from a link on Pricewatch.
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