When considering upgrading your domain controllers to R2 don’t forget that R2 only comes in 64-bit. That means you cannot do an in-place upgrade from the 32-bit version to 64-bit version. You will have to deploy a new server and run the DCPromo wizard. An R2 Server does require Adprep to be run on your existing domain controllers  before it can become part of the domain. If you existing domain controllers are 32-bit then make sure you run adprep32.exe (/forestprep and /domainprep) since adprep.exe is now 64-bit and will not run on 32-bit machines.

Written by Brian Fontanella