The student sites are now NT4 free! I reinstalled the last NT4 BDC with Windows 2003 Server today. I also moved the FSMO roles off the upgraded DC to a clean install server, so next up is to demote the upgraded DC and then reformat and reinstall it.
After that is the upgrade for the admin domain, but that involves an Exchange 5.5 server, so much more testing will be needed before we even start thinking about actually doing that.