Multiple domains form trees within a forest. A tree can be defined as a hierarchical arrangement of Windows Server 2003 (or Windows 2000) domains within a forest. A tree is established when a child domain is added to the hierarchy under an existing parent domain. When you add a new domain as a child domain, it inherits a portion of its namespace from its parent. When you create a new tree within a forest you are establishing a new namespace.

You can create a new tree within a Windows Server 2003 forest using the steps below:

1. On the member server, you want to turn into a domain controller, click Start, and click Run.

2. Type dcpromo and click OK. This launches the Active Directory Installation Wizard. Click Next.
3. Click Next.
4. Select Domain controller for a new domain. Click Next.
5. Select Domain tree in an existing forest. Click Next.
6. Type in the appropriate network credentials (the user account must be a member of the Enterprise Admins group). Click Next.
7. Type in the DNS name for the new domain. Click Next.
8. Click Next to accept the suggested NetBIOS name for the new domain.
9. Click Next to accept the default settings for the database and log locations.
10. Click Next to accept the default settings for the shared system volume.
11. Click Next.
12. Select the permission level you want to use. Click Next.
13. Type in a password for the Directory Services Restore Mode Administrator Password. Click Next.
14. From the Summary dialog box, click Next.
15. Click Finish.
16. Click Restart Now.