Okay, I'm jumping out a step because the replies are getting uncomfortably skinny. 🙂
hatter, if by "Network cp" you mean system Preferences -> Network, I do not have an "Add" button anywhere on that control. The other ports DO NOT show up there, not even as unconfigured.
Further, if I go to System Profiler -> Network, the ports don't show up there either (and again, there is no "Add" button).
Finally, I'm still a little perplexed that the PCI-Express card itself does not show up in the System Profiler -> Hardware -> PCI section. Only my video card shows up.
I know that the other card is plugged in properly because running the PCI Lane configuration tool shows the card (and you're right, I have the card in slot 1, which my configuration has as an 8x lane). There are 4 possible configurations, and I have the first one selected. To the right of each lane bar there's a little light that shows yellow for cards that will be performing beneath optimum and green for cards that have enough lanes to perform at or above optimum. Again, both my video card and my "Unknown Ethernet Controller Card" show green.
So the PCI bus knows there's an Ethernet card there, but none of the other system utilities (System Profiler, System Preferences, etc) seem to be able to see it.
Weird? Totally. Frustrating? You have no idea.