Are these AD domains? I am asking because you mention PDC’s but then you say these are all W2K3 servers. If you are referring to PDC Emulators then the question makes more sense. With AD you can just transfer the role on the PDC Emulator once you promote the new servers to DC’s. AFter that you should be able to DCPROMO the old PDC’s down and remove them from the network.
A couple of things to remember is that the PDC Emulator is your master time source for the domain and if you are pointing the old one to an NTP server some where you will have to accomplish this on the new ones also. The other isssue that can come up is the Domain Master Browser role which is usually configured on the PDC Emulator. You will have to update the registry to reflect TRUE under IsDomain Master under HKLMSYSTEMCurrentControlSetServicesBrowserParameters.
As for the roles of DC’s you should refer to the TechNet web site and look at some of the how to documentation. The W2K3 Resource Kit is available there for download and it has the recomendations.
Hope this helps!