Microsoft Knowledge Base Article 223787 contains the following summary:

This article describes how Flexible Single Master Operations (FSMO) roles are transferred from one domain controller to another and how this role can be forcefully appointed in the event that the domain controller that previously held the role is no longer available.

For more information about FSMO roles in general, please see the following article in the Microsoft Knowledge Base:

197132 Windows 2000 Active Directory FSMO Roles

For additional information about the correct placement of FSMO roles, please see the following article in the Microsoft Knowledge Base:

223346 FSMO Placement and Optimization on Windows 2000 Domains