Determining status of a network connection?

I want to be able to poll the status of a physical network connection. E.g. I want to know if a particular ethernet card is connected (to a hub) or not. I don't care if it could reach other machines or not, I only care about the hardware-level connection.

Essentially, I only care if there is a physical hardware connection to a given NIC. Exactly like the Win2K/XP icons in the taskbar that tell if you're connected or not connected.

What's the easiest way to accomplish this? I've done some reading on SNMP, which seems to have the features I'd need, but none of the sites I've seen or documentation I've read have enough detail to explain how.