Since there is no graphical interface to enter the product key or activate a copy of the Windows Server 2008 Server Core, there are two simple commands to get the job done.

1. Logon to the server core console
2. Enter the product key:  cscript C:\windows\system32\slmgr.vbs -ipk PRODUCT-KEY-HERE
3. Activate:  cscript C:\windows\system32\slmgr.vbs -ato