- Do these services all "port over" to Win2k format?
- Can the BDCs (all running WINS and DHCP) be upgraded to Win2k with AD?
Note that while you only have this one Windows 2000 DC, you have a single point of failure. If that Windows 2000 DC goes down, all of the other Windows NT 4.0 BDCs will stop functioning correctly. So, it is in your best interest to upgrade at least one other BDC immediately after the PDC. Also, note that File Replication will stop working. You can use Resource Kit tools to replicate your NETLOGON share -- but it is a manual process. Finally, if you have any NT 4.0 system policies in place you will need to convert those over to a group policy.
As a final note, any Windows 2000/2003 servers, Windows 2000 workstations or Windows XP workstations will automatically detect that they are now in an Active Directory. They will convert themselves over to using Kerberos and LDAP as opposed to NTLM authentication methods. If you have to drop back to NT 4.0, or the Windows 2000 DC fails before you have another one in place, these machines will have to be removed from the domain manually and then added back in.