Discovering a Computer's Host Name:
One of the most common problems when troubleshooting IP conflicts is discovering who is actually using a specific IP address. You can use one of the built in tools that comes with windows to track down a certain IP address:

Open a command prompt, and type nbtstat -A xxx.xxx.xxx.xxx, where the xxx's represent the IP address your trying to discover. Keep in mind that the '-A' is case sensitive. This command will usually reveal the hostname of the PC that currently owns the given IP address. This command may however return the hostname of the current PC. If this PC is registered with the given IP address, then some PC, if Windows NT or 95/98, is also getting an error attempting to register it's name.

In addition, the System Event log will record an entry citing the offending PC's MAC Address. This can be useful especially if the computer is attached to a Novell server because you can then retrieve the PC's user ID like so:

If on Novell 4.x server:
Open a command prompt, and type nlist user /A | FIND /I "MAC address"

If on Novell 3.x server
Open a command prompt, and type userlist /A | FIND /I "MAC address"

For example:
If I were on a Novell 4.x server and I has a MAC address of 00-08-C7-59-AE-61, I would simply open a command prompt window, and type:
NLIST USER /A | FIND /I "8C759AE61"

If I were on a Novell 3.x server and still had the same MAC address, I would simply open a command prompt window, and type:
USERLIST /A | FIND /I "8C759AE61"

You will notice that I left out the hyphens and leading zeros. With the MAC address you can detect the manufacture of the NIC. For example, my MAC address is "00-08-C7-59-AE-61", the leading six digits, "00-08-C7", tell me that the NIC is assigned to Compaq. This can be useful if for example if the problem is originating from a device such as print server.

Most times when Duplicate IPs occur, it is because some device is using a fixed IP that is also assigned to the DHCP pool. NT DHCP Server offers a facility to "attempt" to detect this situation.

Some times devices that attempt to use DHCP do not follow 'standard' DHCP protocol, and as result cause multiple devices to use the same IP address. Also, if the NT DHCP Server is configured to attempt to detect "BAD" IP addresses it would simply mark them as BAD and assign a different IP. Devices such as printer servers, especially older versions, have this problem.