Upgrading from Windows 2003 to Windows 2008

I think I've got it... I've just rebooted and let it roll back to Server 2003. The DPM managed volumes didn't previously have drive letters but 22 of them now do A-z less X for boot, and A:(floppy),B:(reserved for floppy I think),C: (cd-rom).

I guess the windows upgrade is enumerating the drives and trying to add drive letters where there were none and there are more than 26 drives so it hangs.

Ho hum straight build it is.

Make sure you are using the version of adprep from 2008 R2. It should be run on the schema master and infrastructure master for the domain for /forestprep and /domainprep respectively. Win2008 R2 is 64bit, but it also has a 32bit version of adprep if you need it. (ADPREP32) Yes, it can be run during business hours, and I have never seen them take more than a few seconds to do their jobs.

1. Run adprep /forestprep. Wait for schema changes to replicate.
2. Run adprep /domainprep. Wait for replication.
3. Don't mess with domain and forest functional levels yet.
4. DCPROMO your Win2008R2 box alongside your existing DCs.
5. Transfer FSMO roles to it if you wish.
6. Begin decomissioning your old DCs by first demoting them with DCPROMO.
7. You're done. Your domain and forest functional levels are still at 2003, you simply have a 2008 R2 machine for a domain controller. (You didn't specify exactly what your DFL and FFL was so I assumed.)

Answering your questions:

1. You need to transfer the roles manually as per my instructions above, that is, if your intent is to let the new 2008R2 DC have the FSMOs.

2. Yes, DCPROMO should be all that is required to demote a domain controller. If something goes wrong trying to demote it though you'll have to perform a metadata cleanup. (Not hard.)

3. After all of your old DCs are gone and you have only 2008R2 DCs in your forest, you can start thinking about raising the FFL and DFL.