Dear RickyTan (LOL thats from Rush Hour)
I am not sure on how effective it is, since we only have about 15+ people in our office. However it should work, and I don't think it will bring your network down...Also obviously you can't use this tool if you don't know what your administrators usernames are...Which I doubt is true. So if you know there usernames just sort it by name. You can click the User Column to sort by name and flow through the list. 8k-10k is alot of people so good luck. But this should be able to accomplish what you need although, as long as you know what your looking for sorting it will make you do this fast... And you are also able to close sessions from here.
To Signup,
Are you typing in your domain name with the dot com in it? I am not sure if you can use it as I don't think Windows NT 4.0 uses the new DNS Naming Convention that windows 2000 supports. Windows 2000 new DNS Name Convention is like microsoft.com which is the domain name, as oppose to MICROSOFT. So you won't be able to do this unless your in Native Mode, unless someone knows NT 4.0 better then me, I don't have any NT 4.0 machines in the office to check, but there still might be a way to do it, as I remember there is a Sessions somewhere in Control Panel under a Catergory.
Good Luck