To set up an Office 2010 KMS host on Windows Server 2003, you must install Key Management Service (KMS). Although the minimum required version is KMS 1.1, we recommend that you install KMS 1.2. KMS 1.2 recognizes virtual computers as part of the activation count. If your network contains virtual computers that must be activated through KMS; then download Windows Server 2003 x86, x64 package edition, and then follow the instructions to install KMS 1.2 in Microsoft Knowledge Base article 968915: An update is available that installs Key Management Service (KMS) 1.2 for Windows Server 2003 Service Pack 2 (SP2) and for later versions of Windows Server 2003.
Note that for KMS 1.2, Windows Server 2003 must have at least SP2 installed.
More Info: KB968915