We are using Windows 2000 Advanced Server as our DNS server. How do I prevent others from using DNS server?
I'm not sure what you mean by "how do I prevent others from using DNS?" Do you mean using it to look up a DNS address? There are several ways to limit access to the server, because you typically want DNS lookup to occur. What do you mean by "others"? If the server is entirely private (i.e., there are only internal addresses in it), put it on the internal network and do not allow any access from external network.
If what you mean is how to prevent another, unauthorized zone transfer -- then you can easily configure DNS to allow zone transfer only with those specific computers you identify.
If what you mean is use it for something other than a DNS server, check out the lockdown server information on the Microsoft site. Start here.
Dig Deeper on Windows 10 security and management