i’ve personally only had to go through the adprep process once in 2009 (so far). i figured it would be good to notate the process for future reference though. it came up again recently for a different AD domain…

for introducing a windows 2008 DC:
run the following from the windows 2008 install media on the schema master
d:\sources\adprep\adprep.exe /forestprep

then on the infrastructure master run
adprep /domainprep

notes:
you may need to run the 32-bit version of adprep. also i’m assuming functional levels are at most current (which would be 2003 in this case). when operating at a 2000 functional level extra steps might be necessary. there is another adprep step for preparing the domain for read-only DCs, it’s “adprep /rodcprep”. we had no plans of introducing RODCs so we did not do this step. you’ll get an error in dcdiag for not doing the RODC prep, but it appears that it is okay to ignore it.

the process will be the same for introducing a windows 2008 r2 DC however adprep will be in the d:\support folder on the install media.

also in-place upgrades of domain controllers are supportable by microsoft, but best practices dictates setting up a new DC with the latest version of windows server and decommissioning the older DC. some people say that you should transfer FSMO roles prior to doing an in-place upgrade, however, that doesn’t appear to be necessary.

the five FSMO (flexible single master operation) roles:
PDC emulator
RID (relative ID) master
infrastructure master
schema master
domain naming master

sources:
http://www.petri.co.il/windows-server-2008-adprep.htm
http://www.petri.co.il/prepare-for-server-2008-r2-domain-controller.htm

update 7/23/2014:
windows 2012 domain controllers do not require adprep to be ran manually. in fact, both adprep & dcpromo are taken care of automatically when adding the AD DS role to a windows 2012 system.
further details: http://kpytko.pl/2012/09/07/adding-first-windows-server-2012-domain-controller-within-windows-200320082008r2-network/

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