Windows 2000/2003 Active Directory domains utilize a Single Operation Master method called FSMO (Flexible Single Master Operation), as described in Understanding FSMO Roles in Active Directory.
The five FSMO roles are:

Schema master - Forest-wide and one per forest.
Domain naming master - Forest-wide and one per forest.
RID master - Domain-specific and one for each domain.
PDC - [...]

Windows 2000/2003 Active Directory domains utilize a Single Operation Master method called FSMO (Flexible Single Master Operation), as described in Understanding FSMO Roles in Active Directory.
In most cases an administrator can keep the FSMO role holders (all 5 of them) in the same spot (or actually, on the same DC) as has been configured [...]

Windows 2000/2003 Multi-Master Model
A multi-master enabled database, such as the Active Directory, provides the flexibility of allowing changes to occur at any DC in the enterprise, but it also introduces the possibility of conflicts that can potentially lead to problems once the data is replicated to the rest of the enterprise. One way Windows 2000/2003 [...]

Have you seen the Microsoft Active Directory 70-640 Training video by Train Signal? I highly recommend this course, as you will learn much more than you will from any book. It includes new iPod/MP3 versions of the course (when you are on the go) and Transcender practice tests to help you prepare for certification. The [...]

Welcome to the 15th installment of Learn Active Directory Design and Administration in 15 Minutes a Week, a weekly series aimed at current IT professionals preparing to write the new Windows Active Directory Design and Administration exams (70-219 and 70-217 respectively), as well as newcomers to the field who are trying to get a solid [...]

I) Forest-Wide Operations Master Roles
Every Active Directory forest must have the following roles:
¦ Schema master
¦ Domain naming master
These roles must be unique in the forest. This means that throughout the entire forest, there can be only one schema master and one domain naming master.
1) Schema Master Role
The domain controller assigned the schema master role controls [...]

There are certain Flexible Single Masters of Operation (FSMO) roles that are Forest Wide Operations Master Roles. This means that no matter how many domains exist in the forest, you will only have one of the those particular FSMO servers in the forest.
The Schema Master Domain Controller handles all of the updates and modifications to [...]