Replacing existing 2003 server

I am going to be replacing the 2003 server in our environment. This is the only server and is the AD and fileserver. It is currently 2003, and I will be replacing the server hardware and upgrading to 2003R2. Are there any tech docs or items I must be aware of before doing this? I have only added servers to a network, not replaced one that is the primary server…so help is needed.