Before we launch into a discussion of how to troubleshoot a DNS problem, we should make sure you know how to tell whether a problem is caused by DNS, not by another naming service. On Windows hosts, figuring out whether the culprit is actually DNS can be difficult. Windows supports a whole panoply of naming services: DNS, WINS, HOSTS, LMHOSTS, and more. The stock Windows Server 2003 version of nslookup, however, doesn't pay any attention to these other naming services. You can run nslookup on a Windows Server 2003 box and query the name server til the cows come home while the service with the problem is using a different naming service.
How do you know where to put the blame? First, you need to consider what kind of program is having the problem. If it's a TCP/IP client, such as telnet or ftp, the possible culprits are DNS and the HOSTS file. If it's a utility that supports NetBIOS naming, such as net (as in net use), the likely suspects also include WINS and the LMHOSTS file. Other clients, such as ping, that also take either a DNS name or a NetBIOS name as an argument can use any of these naming services.
Next, consider the order in which Windows uses the naming services. You should look through the various services in that order when troubleshooting the problem.
These hints should help you identify the guilty party or at least exonerate one suspect. If you narrow down the suspects and DNS is still implicated, you'll just have to read this chapter.