I should clarify this issue further.
OEM licenses - there are two types. One is SLP (System Locked
Preinstallation), the other one is personal.
OEM SLP licenses are licensed by MS to PC manufacturing companies
such as HP, Dell, Acer, IBM, etc. All these license keys are
trained to work only on certain hardware. In other words, it's
already part of the BIOS and the installation CD. That's the reason
why such discs will never work on another machine if you attempt to
reformat and reinstall Windows.
The personal OEM licenses are sold to retailers or distributors,
which are then bought users themselves. Commonly used by DIY PC
users or those branded PC users who don't like recovery CDs due to
the junk these PC manufacturers install and a lack of features
which only installation CDs could do.
Corporate licenses, or VLK (Volume Licensed Keys) are licensed to
huge corporations or educational institutes. For XP, Office 2000,
Office XP and Office 2003, you just need to enter this key. There's
no need to write down so many keys for the different PCs.
For those who use XP and above... you will notice some
database-like files in the system32 folder. These database-like
files are actually your hardware details, binded to the MS license
key.
This is also one reason why you can't keep upgrading your PC
hardware... after it reaches a certain threshold, it will be deemed
as a new PC using an already activated license key. You have to
call up MS to re-activate your copy of Windows.
For the curious, only OEM licenses have their hardware binded to
the licenses, it doesn't affect VLK.
Starting from Vista... VLK will need to be confirmed with the
servers at MS. The reason is because VLK has been abused in XP. One
key can install lots of legitimate copies of Windows XP.
He can post the key for all he likes, it won't affect anyway...
because it can't be activated. MS already closed this loophole.
Unless... as I've said, the hardware details matches. But that is
no guarantee due to the BIOS. The CDs and OS are very well-trained
in this aspect.