If you know the chipset that your Ethernet adapter uses, this is easy. If you have the NS8390 chipset, or a NS8390 based chipset, use nb8390.com. If you have a 3Com® 509 based chipset, use the nb3C509.com boot program. If you are not sure which you have, try using one, if it says “No adapter found”, try the other. Beyond that, you are pretty much on your own.