Hardware Project 1 - Diskless XP

Software: Richtech V3.0
Hardware: 1 server, 2 station
found station motherboard GE PRO-M2 doesn't support. P4VM800 and P4i65G support.
found station domain login is fake.
Question: if server full name is "xxxserver.server.abc.com", it installed active directory, what's the domain for this server? For example, when I use a station to login, I want the server's active directory to control the username and password. What's the domain I should use in order to use the Active directory? I tried "xxx.server.server.abc.com", "server.abc.com", "abc.com" all doesn't work, but I tried "server", it works. So the domian should be "server". When I relogin, if I tried to use "server" as domain, I can't login. I have to use "station00" instead of "server" to login, so why I can login use "server" as a domain at the first time, but I can't use "server" to login now.