I have always found Device Manager (Control Panel --> System, I believe in NT4) to be helpful in identifying this.
Also, with NT4, on some systems, I found I had to:
1 - load NT4 with no NIC in the box
2 - shutdown and physically install card
3 - reboot and shutdown (P&P seemed useless, but this clears up any memory cache etc.)
4 - reboot and manually install drivers
At that point the NIC was generally picked up by the manual install. If not, then it was back to Device Manager to lookfor device (e.g., IRQ) conflicts.
Sometimes you can manage IRQ conflicts by changing the settings, and sometimes, it needed the box opened up and the PCI cards shuffled around.
Good Luck