As per adding XP machines in windows 2000 with uprooting and using AD will
change the concept of domain.
a domain is a security boundary in which we have users and group which are
managed centrally. what you can try is to keep all the users in workgroup.
they will be able to gain access to the resources. also if you want your
users to use to work on windows 2000 server then you can enable Terminal
Serveices.