ADPREP ForestPrep

I am trying to install AD on 2003 server in a 2000 Domain. I ran the ADPrep forestprep on the 2000 server with schema master. I ran the adprep domainprep on the same server as the master. I tried to install AD on the 2003 and I am getting the same message that my forest is not ready and I will need to run ADprep forestprep. I tried and it says that the forest has already been preped and can not do it again. Please help