Child Domain

Hello,
We are running windows 2003 service pack1, we have a child domain already inplaced. Now we bought a new server2003 R2. I am planning to join as a child domain with the existing domain and delete the existing child domain.
I ran dcpromo on new server(2003R2), I am getting error messages as follows:
Tha active directory wizard cannot continue because the forest is not prepared like that…
The version of the active directory schema of the source forest is not compatable with the version of active directory with this computer.
I am seraching on this one, but i am not clear
How to use this tool. Do i need to run on forest, what are causes- please help me
thanks,
Suresh