if you go to start menu, select run and type winipcfg on a 98 machine you will get the MAC address of the NIC. On 2000 and NT, type ipconfig in a DOS box. I personally look at the card, identify an important looking IC (usually the great big fat one in the middle) and do an internet search. I also look at stickers on the cards that have serial-like numbers and do searches on them too. More often than not, the name of the Manufacturer is printed on the card anyway.
This reminds me of when I used to have a PCI soft-modem, ah, the joy I had trying to remember the name of the manufacturer of the modem when it came to reinstall time (was it Spasmotron or Wankotech? I can never remember). I've found in Linux it easier because people write drivers for chipsets instead of specific cards.