To catch a thief

I have a wireless school network. Am running W2K server and the clients are W98. Some of the lan cards have been stolen and I need to try to find or disable them.

1) Is there a way to trace the card back through the hub it is using?

2) Is there a way to set up an alert when the card signs on?

3) Is there a way to block the NIC address from accessing the network?

An help would be appreciated.