If you are getting lights on the card it means your pci slot is providing the power the card needs. The card is also determining that you have a 100Mbit ethernet network.
You may have an IRQ conflict. Try reserving an IRQ for the slot your ethernet card is plugged into. What can happen is the BIOS can assign the same IRQ to 2 different devices and this can cause conflicts. Also try removing any other cards you don't need, like sound cards or modems. You should just have the ethernet card and a video card if video isn't built into the motherboard.
Disable everything you can in the BIOS, stuff like on board sound, modem, printer ports, serial ports, etc. This will help free up resources.
As far as plug and play in the BIOS, try it each way and see what happens
You might also see if there are any wait state or speed settings for pci in the BIOS.
Are you able to get the ethernet cards to work in another machine? It could be you have bad cards.
If you're planning on using the NASLite pc as a network drive for Windows you only need to use the SMB or SMB-G versions of the floppies. The 3 G versions should all use the same ethernet driver so there's no need to try each version.
What motherboard brand/model/version do you have?