The Unleashed series of books are generally pretty good. I have a standard 2008 book, and its not too bad.
One note, there are no primary domain controllers anymore. The closest you'll find to any sort of setup like that in 2008 is that there are now Read-Only domain controllers (good for sites with slow links).
Dont forget to transfer the server roles like infrastructure master and such before removing the old servers. absolutely critical but very easy to overlook. You find them by right clicking on the domain in Users & Computers. Transfer them on the server you want to move them too.
Its actually a good idea to read up on this since you'll want to move the roles in an appropriate manner, because the are very important and can have a huge impact on the structure of your domain.
