Although 2000 doesn’t have a “primary domain controller” in the sense NT did, you have several “FSMO” roles to consider. Check out this link: http://support.microsoft.com/kb/324801
As far as promoting to a domain controller, see the instructions at this link: http://support.microsoft.com/kb/238369
If you are still running with a legacy NT type structure, this cookbook may be helpful:
Let me know if you have a specific question.