How to Join Windows Server 2008 to Active Directory Domain
Log on to windows server and open Server Manager.
Under Server Summary, click change system properties option as shown above.
Select Computer Name tab. Click change button as shown above.
Under member of option, choose domain and type the domain name. Here mustbegeek.com is the domain name. Click OK.
Enter domain administrator credential and click OK.
Click OK and reboot the server. The server is now joined to domain. You can now logon to server with domain credentials. You can open Server Manager to verify if the server is joined to domain.
As you can see above the server is joined to domain. In this way, you can join Windows Server 2008 to Active Directory domain.