I've got a newish Windows 2003 DC and a very old Windows 2000 DC running together in Windows 2000 Native mode. I've got to pull the 2000 Server to repair it, so I want to add in a temporary 2000 Server to keep 2 DCs running. When I run DCPROMO on the temporary box, will it get the correct schema from the 2003 Server? Or do I have to run adprep /forestprep and adprep /domainprep before I add it to the domain?
Dcpromo is really all you should need. [ad|forest]prep is only needed when upgrading the schema, which you're not doing at this time.
Additionally, if an [ad|forest]prep operation is ever needed, windows is usually good about notifying you as such.
You only need to use adprep on the 2000 Server if you want to move to a 2003 functional level.