Having trouble with computer name in ActiveDirectory

I have a Mac running OS X Snow Leopard. I have bound this computer to our Windows Server network using Active Directory. For some reason the local computer name is not matching the network/DNS name.

My Computer Name is: "big-brain" so computers on our local network can access it at: "big-brain.local"

Under file sharing and on our network I want the computer to appear as "big-brain.ourdomainname.com" however it appears as "some-random-name.ourdomainname.com."

How can I change this? I have checked quite a few settings, but can't seem to find the winning combination.