Windows AD dcpromo /demote, who gets the roles?
Solution 1:
From one of the DCs run netdom query /domain:<yourdomain> fsmo to find what servers hold what roles. Then manually Transfer any roles the 2000 server holds as per: How to view and transfer FSMO Roles
Solution 2:
It won't happen automatically, you will need to move the roles manually to the server that will be the new role holder.
Solution 3:
Transfer the FSMO roles to your Win2K3 server, see:
How to view and transfer FSMO roles in Windows Server 2003
How to view and transfer FSMO roles in the graphical user interface