Is the network card functional?

To determine whether or not the network card is functional, i.e., transmitting and receiving packets, use the nicinfo command.

If you're logged in as root, your PATH includes the directory that contains the nicinfo executable; if you're logged in as another user, you have to specify the full path:

$ /usr/sbin/nicinfo

Now figure out the diagnostic information from the following output:

en0: 
  AMD PCNET-32 Ethernet Controller

  Physical Node ID ........................... 000C29 DD3528
  Current Physical Node ID ................... 000C29 DD3528
  Current Operation Rate ..................... 10.00 Mb/s
  Active Interface Type ...................... UTP
  Maximum Transmittable data Unit ............ 1514
  Maximum Receivable data Unit ............... 1514
  Hardware Interrupt ......................... 0x9
  I/O Aperture ............................... 0x1080 - 0x10ff
  Memory Aperture ............................ 0x0
  Promiscuous Mode ........................... Off
  Multicast Support .......................... Enabled

  Packets Transmitted OK ..................... 588
  Bytes Transmitted OK ....................... 103721
  Memory Allocation Failures on Transmit ..... 0

  Packets Received OK ........................ 11639
  Bytes Received OK .......................... 934712
  Memory Allocation Failures on Receive ...... 0

  Single Collisions on Transmit .............. 0
  Deferred Transmits ......................... 0
  Late Collision on Transmit errors .......... 0
  Transmits aborted (excessive collisions) ... 0
  Transmit Underruns ......................... 0
  No Carrier on Transmit ..................... 0
  Receive Alignment errors ................... 0
  Received packets with CRC errors ........... 0
  Packets Dropped on receive ................. 0

You should take special note of the Packets Transmitted OK and Packets Received OK counters. If they're zero, the driver might not be working, or the network might not be connected. Verify that the driver has correctly auto-detected the Current Operation Rate.