Domain Name System (DNS) is a database system that translates a computer’s fully qualified domain name into an IP address. To correct DNS settings and troubleshoot DNS problems, you can

1. Run nslookup from a command line is the default dns server the one you expect.
2.  use ipconfig /all on client to make sure the client point to correct DNS server and the the DC server points to only itself for DNS by its actual tcp/ip address, and make sure no any ISP DNS  listed in tcp/ip properties of any W2K/XP.
3. When the machine loads it should register itself with the DNS. If not, use ipconfig /regiesterdns command.
4.  Check Event Viewer to see whether the event logs contain any error information. On both the client and the server, check the System log for failures during the logon process. Also, check the Directory Service logs on the server and the DNS logs on the DNS server.
5. Use the nltest /dsgetdc: domainname command to verify that a domain controller can be located for a specific domain. The NLTest tool is installed with the Windows XP support tools.
6. If you suspect that a particular domain controller has problems, turn on the Netlogon debug logging. Use the NLTest utility by typing nltest /dbflag:0x2000ffff at a command prompt. The information is logged in the Debug folder in the Netlogon.log file.
7. Use DC Diagnosis tool, dcdiag /v to diagnose any errors. If you still have not isolated the problem, use Network Monitor to monitor network traffic between the client and the domain controller.