Locating username from the computer name

If they're using any shares on that server, you can use Server Manager. Open it, Dbl-Click the server, then click on Users or Shares. This should tell you who they are and how long they've been there.

Hope this helps.

I tried the Server Manager/Users and Shares. It tells me what users (their usernames) are currently connected but it doesn't let me know their computer name.

I have a computer name and its IP address, but I don't know who is logged onto the computer and where it is located.

I'm not sure but I think that if you use DHCP/WINS then on the DHCP/WINS server you can also see who the user is.
Hope this helps.

at the command prompt type.

Nbtstat -A (Stations ip address)
or
Nbtstat -a (stations Netbios Name)

Answer 3 pretty much sums it up, but the node that you are looking for is the one lists as <03> or the messenger Service. Refer to the following articles if you want to read more about Nbtstat :

http://support.microsoft.com/support/kb/articles/Q119/4/95.ASP
http://support.microsoft.com/support/kb/articles/Q163/4/09.ASP

From the tone of the question it sounds like this user is doing ?something Bad.? If you catch them while they are doing whatever, send them a net send message to the <03> name saying that they are busted, so on.

Example:
C:\> Nbtstat ?A 192.168.1.123

?.
Username1 <03> Unique registered
?.

C:\>net send Username1 I finally busted you in the act. Call extension 1320 to discuss immediate termination!

Beef