Workstations do not read the Domain Controller

Hello,

I'm trying to create a test workstation to simulate the environment that exists at my workplace.

I have a Windows Server 2003 with Active Directory installed, it works.

These are the IPs I used:

IP:                          192.168.120.253

Subnet Mask:          255.255.255.0

Default Gateway:      192.168.120.254

Preffered DNS:          192.168.120.253

Also I have a normal Windows 7 that is connected to the domain with permissions, works properly. Main server can read it just fine and it joined the Domain without a glitch.

I've given this one the IP 192.168.120.50

Now I'm trying to create 2 more servers: SQL and Web. I've installed Windows Server 2003 on both of them.

I've given them 192.168.120.70 and 192.168.120.80

but they won't read the main server nor will the server read them and so I can't join them to the domain.

Any advise on this one? Thanks.