As mentioned in our previous blog about user rights, which has become a hot topic as many upgrade to the new Windows 7 platform, OEM licenses cannot be transferred from one PC to another. Therefore, they cannot be used to upgrade to a Windows 7 upgrade on another PC. OEM licenses are locked to the original PC it is installed on and cannot be transferred to any other PC.
There is one exception: you can add Software Assurance to qualifying OEM Office and OEM Server licenses within 90 days of the OEM software purchase to be able to receive transfer rights for those licenses. This will not cover the OEM Windows license however.