BleepingComputer.com: Unable to RDP to W2K Server DC from XP/Vista Clients

I have a home network that I administer, and it belongs to a domain that includes a Vista Ultimate machine and several XP-SP3 clients. The domain controller runs Windows 2000 Advanced Server SP4 which has been in place for at least 6 years, and it's role is also DNS server that forwards to my ISP's DNS servers. Terminal Services is setup in administrative mode.

Some months ago I attempted to apply changes to then reset user rights in the Default Domain Controllers Group Policy object( MS KB Q267553), and I believe that the reset caused problems that preclude domain users from connecting to the domain controller via RDP, but I can't be certain of that since I did not test RDP before resetting the GPO. Since then and whenever I attempt to RDP to the server from any domain & non-domain client I get "The Client could not connect to the remote computer..."

Recently I tried resetting security settings in the default Domain GPO in Windows 2000 using the following Microsoft KB article :http://support.microsoft.com/kb/226243 and got the same results.

Just to fill in some blanks; There is a Sonicwall TZ170 between the internet and the LAN. The wired network has a combination of 100Mbs & 1Gbs devices, and perhaps 1 or 2 10Mbs print servers. The version of RDP is a mix of 6.1 and 6.0

Given the steps I've taken, am I now at a point where I need to address each client to fix this? And if so then how is this best done?

The path I've taken leads me to these questions, however I'm open to any premise out there - I need ideas short of rebuilding the server - or re-joining PC's.

Thanks!