We currently have about 6-8 Server 2003 Domain Controllers in our network. We have created two Server 2008 R2 servers that we plan to promote to DCs as well, make one of them the FMSO, in the hopes of raising the functional level of the domain to 2008 level.
Is it possible to do all this while leaving the 2003 DCs in place? Some of these DCs are in branch offices that will take some time to get to before they can be upgraded to Server 2008 or replaced entirely (some are not 64-bit capable). What are the ramifications in leaving them in production?