Chris,
I know many ISA NE2000 compliant network card with Plug-and-Play function. Since you did not mention your card I had to guess.
The first try I'd do is to change the driver start type. Particularly for the "NE2000 Compatible ISAPNP Ethernet Adapter (Generic)"
component, if you go to its Resource section and open "Novell/Eagle NE2000 Adapter Driver" service item properties, you will notice
that the service StartType is set to "3" (by demand). I'd change it to "2" (Auto).
The same experiment, of course, you could do at run time. Just find appropriate "Novell/Eagle NE2000 Adapter Driver" service under
[HKLM\SYSTEM\CurrentControlSet\Services] and change its "Start" dword value, reboot and see if it helps.
If it is non PnP card, you can also install it on XP Pro machine, grab the appropriate registry entries and include them in to your
image.
The easiest way (if you don't know what keys you should be grabbing) would be using tools like Inctrl5 or (better) RegSnap to
monitor the installation and get the necessary entries.