OK, lets start with a lesson on exactly what a domain is:
Domains are called Active Directories in Windows 2000 and .NET Servers. Active Directory, which is an essential component of the Windows 2000 architecture, presents organizations with a directory service designed for distributed computing environments. Active Directory allows organizations to centrally manage and share information on network resources and users while acting as the central authority for network security. In addition to providing comprehensive directory services to a Windows environment, Active Directory is designed to be a consolidation point for isolating, migrating, centrally managing, and reducing the number of directories that companies require.
You don't just join a domain, and there are not internet domains. Domains are logging into servers on a LAN in a business enviroment. You can't just join one unless there is a seperate Windows 2000 or .NET Active Directory controller on your LAN