Windows Server 2003 is quite different from Windows 2000. In fact, you'll notice that it is more like Windows XP SP2. With that in mind, you should take a look at the firewall setting on the 2003 machine, as this could be preventing some communication issues within the domain.
Also, what is the function on this 2003 server? I assume that it is obviously the DC, correct? Is it also the proxy?
_________________________
It's most likely a problem with your flux capacitor.