If you workstations are locked inside the network, you can basically use any domain you like. You don't have to run a DNS service if you are running ISPC internally. But if you choose, you may
For every Windows workstation you have, edit the HOSTS file with a text editor like notepad. The HOSTS file is found in: \windows\system32\drivers\etc\ and add the fallowing..
<IP of linux server> <domain.name.com>
192.168.0.1 microsoft.com www.microsoft.com
So, each workstation knows that microsoft.com is at IP address 192.168.0.1. It doesn't have to be connected to the internet. Of course the domain will have to change if you want to make it accessable to people outside of your network.