Domain change and DHCP

Hi

I have 2 problems

1) i am Having a windows 2000 server (ABC), which is a domain controller for the domain (XYZ)
Currently DHCP is not installed , can i install DHCP with out reinstalleing windows 200 server

2) the same server (ABC), which is a domain controller for the domain (XYZ)
i need to change the Domain name to ” EFG ” from XYZ
i mean i need to Rename the Domain,( not cahnging the Domain)

is it possible with out reinstalling ??

and if i need to, Reinstall the server, How can i copy the User rights and settings