Windows DC

I am trying to install a Windows 2003 server as a DC in a Windows 2000 domain. No luck. The error is listed below. Can anybody help me out please!!!

THE ERROR MESSAGE
“The problem Failed because: The Active directory installation wizard cannot continue because the forest is not prepered for installing Windows server 2003. Use the Adprep command line tool to prepare both the forest and the domain.”

“The version of the Active directory Schema of the source forest is not compactible with the version of Active directory on this computer.”