1. Verify the new server's TCP/IP configuration has been pointed to the current DNS server.
2. Make the new server become a member server of the current Windows Server 2003 domain first.
3. Upgrade the Windows Server 2003 forest schema to Windows Server 2008 schema with the "adprep /forestprep" command on old server.
Please run the "adprep.exe /forestprep" command from the Windows Server 2008 installation disk on the schema master. To do this, insert the Windows Server 2008 installation disk, and then type the following command:
Drive:\sources\ADPREP\adprep.exe /forestprep
4. Upgrade the Windows 2003 domain schema with the "adprep /domainprep" command on old server.
Please run the "adprep.exe /domainprep" command from the Windows Server 2008 installation disk on the infrastructure master. To do this, insert the Windows Server 2008 installation disk, and then type the following command:
Drive:\sources\ADPREP \adprep.exe /domainprep
5. Insert Windows Server 2008 Installation Disc in the new server.
6. Run "dcpromo" on new server to promote it as an additional domain controller in existing Windows 2003 domain, afterwards you may verify the installation of Active Directory.
Please refer to:
How to Verify an Active Directory Installation in Windows Server 2003
7. Verify the new server's TCP/IP configuration has been pointed to current DNS server.
8. Enable Global Catalog on new server and manually Check Replication Topology and afterwards manually trigger replication (Replicate Now) to synchronize Active Directory database between 2 replicas.
Please note: It will some time to replicate GC between DC, please wait some time with patience.
9. Disable Global Catalog on the old DC.
10. Transfer all the FSMO roles from the old DC to the new DC.
Please refer to:
How to view and transfer FSMO roles in Windows Server 2003
11. Verify that the old DNS Server Zone type is Active Directory-Integrated. If not, please refer to:
How To: Convert DNS Primary Server to Active Directory Integrated
Note: Active Directory Integrated-Zone is available only if DNS server is a domain controller.
12. Install DNS component on new server and configure it as a new DNS Server (Active Directory Integrated-Zone is preferred). All the DNS configuration should be replicated to the new DNS server with Active Directory Replication.
13. Make all the clients change TCP/IP configuration to point to new server as DNS.
14. You may configure TCP/IP on all the clients, or adjust DHCP scope settings to make them use the new DNS server.