Introducing the first Windows Server 2008 R2 DC into a Server 2003 domain.

1. Firstly ensure that all DC's are 2003 and decomission any older versions e.g. NT 4.0, 2000 etc.

2. Raise the domain functional level to 'Windows Server 2003' by going to 'AD Domains and Trusts' MMC snapin and right-hand clicking the domain node and select "Raise Domain Functional Level..."

3. Find out which DC holds the schema and infrastructure FSMO roles:

http://blog.manton.im/2015/02/how-to-query-and-move-fsmo-roles-with.html

4. Ensure that there are no outstanding issues with the domain / forest with dcdiag e.g.:

dcdiag /v

and ensure that replication is happening successfully with:

repadmin /showrepl /all /verbose

5. Run the adprep tool on the DC with the above to FSMO roles - the AD prep tool can be found within the 'support\adprep' folder on the root of the Server 2008 R2 disk.

There are too version - adprep.exe (for 64bit OS's) and adprep32 (for 32bit OS's).

** NOTE: You should ensure that the user context launching the adprep tool is a member of the 'Schema Admins', "Enterprise Admins" and "Domain Admins' security group in A.D **

*** WARNING: Before performing something like this it is imporant that (if possible) you can perform this in a similar on ideally mirrored development environment before making changes to the schema OR at least making a backup of AD firstly! ***

So we shall copy the adprep folder directly onto the Server 2003 host and login with the user who hold the schema admin privilages and run the following:

adprep32 /forestprep

or

adprep /forestprep

We can now OPTIONALLY run the 'adprep32 /rodcprep' statement that will prepare the domain / forest for read-only DC's (a feature introudced in Server 2008) with:

adprep32 /rodcprep

And then proceed by preparing the domain with:

adprep32 /domainprep /gpprep

Once this has completed we can then promote our Windows Server 2008 DC's successfully!