basically you need to register your domain name with internic, they will ask for 2 dns servers, or, 2 public ip address that will point to your 2 dns servers.
why 2 dns server ? they want your servers to be redundant
after that you will need to create a DNS zone, usually the DNS zone is a private ip address (192.something), for instance, create a dns zone with the name of mycompany.com with ip address of 192.168.10.x
w2k will create the forward lookup and reverse lookup zone for you, however if you use NT, you need to create them by yourself.
that's it, if you want someone to be able to access mycomputer.mycompany.com,
you'll need to create a host record that will point to the ip address of mycomputer, dns will add the remaining .mycompany.com automatically
hope this helps,
do buy a book on dns, it really helps