OK, I see the issue now, I was under the impression they were just 2 different ethernet cards.

As I understand it your physical situation doesn't allow you to just tape a cat5 cable on the end of the existing telephone wires, and pull it through where the telephone line is by pulling on the phone wire, then crimp on the modular connectors on each end of the cat5. Too bad, that would be the best and simplest way to do it.

Sounds like the adapter card for this needs special drivers and they are not included in Knoppix. And you may not even be able to find the drivers for your particular hardware version. Not that Knoppix is particularly friendly to adding drivers anyway.

I'm guessing that you have already considered a wireless connection to Slug, but that the thickness of the floors is making wireless unsuitable. If that's the case you might get somewhere with high gain directional antennas. But wifi is what it is, and sometimes it's tough to get the signals where you want them.

I do occasionally see special equipment that is designed to meet this need. I've seen ethernet-to-AC-wiring adapters that just let you plug in an ethernet cable to each adapter, plug the adapter in the wall, and you have ethernet running over your power lines. I've even seen them cheap when on a special sale, but otherwise they can be pricey. The key here is getting something that uses a normal ethernet connection and does the special magic in external hardware, rather than something like the cards you have that need special drivers that may not be produced for all OSs or ever for future versions of Windows.

Good luck. My choice would be to re-look at the options for running CAT5 or to see if I couldn't get a wireless signal through, but with some searching you might be able to find drivers for your hardware. If you go that route and want a Linux system installed upstairs, then I would urge that you go with Debian or some other system intended for hard disk rather than Knoppix, it will make a lot of things, including installing the drivers, much cleaner.