Unable to map a network drive from a Windows NT PC, to a Windows 2000 PC

I am trying to set up a test rack of legacy satellite communications equipment, and part of the configuration requires that I map a network drive on a PC (in this case, it's an IBM eServer xSeries 305 running Windows 2000 Professional), pointing to a device (a very old IP encapsulator) which is running Windows NT.

I know from old documentation that mapping the network drive on a Windows XP machine, pointing to this specific model of Windows NT device (running the identical release of Windows NT), was possible. However, I have no Windows XP machine, and no documentation which would imply that the Windows 2000 configuration would work differently.

When I try to map the drive on the Windows 2000 machine, using the "Map Network Drive" dialog in "My Computer", I get the error "The Remote Computer is not available". If I intentionally attempt to map to a nonexistent IP address, it will instead return "The network path cannot be found."

The two devices are in the same VLAN, and the same network, connected by switchports on a router. On the Windows 2000 PC, I can open a VNC connection to the Windows NT device with no problem.

I've found a handful of troubleshooting steps online which were applicable, but didn't resolve the issue:

1. The "Server" service is running on the Windows NT machine.
2. The target drives and folders are shared with "Everyone" on the Windows NT machine.
3. Enabling or disabling "File and Printer Sharing" on the Windows 2000 machine has no effect.
4. Placing both devices into the same workgroup had no effect.

I understand that this may be too narrow of a problem for this site, so to frame the issue in a broader sense, here's what I'm looking for:

1. Is there any method of mapping a network drive which will generate a more useful/specific error than "The remote computer is not available"?
2. Is there a backwards-compatibility limitation with mapping network drives between different versions of Windows (especially pre- Windows 7)?
3. If there is a backwards-compatibility limitation, can it be overcome?

I appreciate any information to those three broad questions, or any advice about my specific issue which could help me narrow down the problem.