To configure a Windows 2000/2003 Domain Controller as a GC server, perform the following steps:
1. Start the Microsoft Management Console (MMC) Active Directory Sites and
Services Manager. (From the Start menu, select Programs, Administrative Tools,
Active Directory Sites and Services Manager).
2. Select the Sites branch.
3. Select the site that owns the server, and expand the Servers branch.
4. Select the server you want to configure.
5. Right-click NTDS Settings, and select Properties
6. Select or clear the Global Catalog Server checkbox, which the Screen shows.
7. Click Apply, OK.
You must allow for the GC to replicate itself throughout the forest. This process might take anywhere between 10-15 minutes to even several days, all depending on your AD infrastructure.