I know it's possible to use system state, but I do not want to do a full system backup... I want to backup AD and that's it. Would stopping all AD services, then backing up all NTDS files be sufficient in a catastrophic failure? Would I be able to just copy/paste in my "backup" copies of the NTDS files?
This is a terrific idea! Terrifically bad!
You'll need to backup your registry, SYSVOL folder, Ntds.dit, Edb.chk, Edb*.log, Res1.log and Res2.log. Oh, but that's not all! If there are other domain controllers in the domain you'll have to worry about non-authoritative versus authoritative restores. Just try doing that without a proper, "Microsoft Sanctioned" backup.
Let's Have Some Fun!
Since no one should ever consider their backups to be good enough until they've performed a fully functioning restoration, you go ahead and back up your Active Directory the way that you proposed above. Then, try and restore it. Tell us how it went.
I mean, you'll be performing full test restorations anyway, right?
We'll wait for your return.
Why not just use the built-in backup utility to do a backup of the system state? That will get all the key files that you need. It's not a full system backup, and it shouldn't be too large.