>>We have WIN SERVER 2003 as our Domain Controller in a single domain environment and we want to setup a server running WIN SERVER 2008 to operate as a backup domain controller in case WIN SERVER 2003 goes down. How do we set that up?
>
>Add the domain controller role to the server.

In Server 2008 There are many roles listed:
We have checked :
Active Directory Domain Services

What about the other roles, do we need them?
DNS Server, Active Directory Certificate Services, Active Directory Federation Services,
Active Directory Lightweight Directory Services, Active Directory Rights Management Services

We will need this additional server to be our backup domain controller.

Thanks