*** Improved by Wrobinson on 03/16/2008 ***
First of all, what does the source domain contain, such as users, files applications and so on? The answers to these questions will determine what is and isn’t possible and how to proceed. You need to provide more details in order for this question to be answered completely.
*** End Update ***
yes, if it is a DC you would need to do a dcpromo to demote the server to a member server. then dis-join it from the domain. Then join the new domain and promote it to a DC again.
It is isn’t a domain controller then simply right click on My Computer and select properties and change the domain. You can add a CNAME entry in DNS in the old domain to help users in the old domain find the server in the new domain without having to know the full DNS name of the server.