I have added my windows 2003 server under a domain. I want to add users and groups by using computer management. But when I add domain to server, that local users & groups tab not coming in Computer management tab. How I can bring that in computer management?

If the server is acting as an Active Directory Controller in the domain/forest then you must use Active Directory Users & Computers management console plugin to manage users. This is usually found under Administrative Tools nested below the control panel. If the server has only been added to the domain you should still see Users & Groups in the computer management console. Have you assigned a role to this server? AD? Then it seems the first applies.

Dear Dewd,
Thanks for your reply. I have added domain to the server, but I can't see the Users&Groups in the computer management. Is it necessary for Windows 2003 Failover clustering?