to save my Server from internal attacks

HI, I just wanted to know if i could save my server from internal attacks? We have a hardware fairewall in our network so hacker attacks from outside is no problem. My files have been deleted by a user in my network. I have a member server NT4.0 where i handle all user accounts. I have “unshared” all my partitions from my system and hide my hostname from the network systems list but they still can search my system and then were able to enter and delete some of my files.

Please tell me some good security settings or software that may give me “Authentic Security” or near it atleast. PLease Helpppppppppp