Changing the winlogon dialog box

We have a network with 5 NT4 servers and about 150 NT4 Workstation clients. We share this network with some other companies.
When the workstations login they got a dialog box where the user has to fill in his name, password and domain.
We would like that the domain name to be invisible (for normal users: not the administrators). Is there a way to change the winlogon dialog box?
It has to do with the gina.dll i found out on the internet.
Can someone help?