I'm having a problem with a windows server 2008 server. After it was demoted from a AD domain controller, it is unable to get to the login screen (it reboots after applying user settings).
Is there a way to recover files from this system via something like a windows live CD, or of course fix this issue?
You need to provide a bit more information. Does the computer have a RAID controller? Is it hardware or software based? Is it simple mirroring, or something like RAID 5?
On a single disk or mirrored disk configuration, you can just take the harddrive out and put it into a different computer to access the files.
If it's a more complex setup, you'll need to keep the array intact. Since the system is still booting, you can probably access the files through any normal boot environment. My preference is an Ubuntu Live CD. It's a bit tricky, but you can access NTFS partitions and then transfer data over the network. Alternately, you could move the drives and their RAID controller into another machine all together, but that's a slightly riskier proposition.
Use Knoppix. Seeing that the machine gets to the stage where it wants to apply user settings, it is unlikely that there is a problem with the hardware, and Knoppix should boot straight up. I am not aware of a Windows Live CD.
Moving drives and RAID controllers is a tricky thing. I've tried this in the past, and more often than not, it doesn't work.
You should also be able to boot from the Windows install CD into a rescue mode and then perform some basic rescue operations, although your network connectivity in rescue mode is difficult.
Does Safe Mode work? Have you tried logging in as another account? I second the booting with the network cable unplugged and cached credentials.
Worse case, a repair install or even try to restore a backup from when it was a DC (but off the network of course).