How to force Ubunto to redect the network card

[Vaughn Treude]

Hello all,
Thanks to the your help with my CPU heating problem, I have that
troublesome system of mine rebuilt.  The reason I had to reinstall the
CPU was that I replaced the existing ABit motherboard (which I believe
has a problem that causes it to lose power sporadically) with a Soyo
motherboard with the same sort of socket.  Most of the hardware other
than that I left the same, including the hard drives which had Ubuntu as
the default bootup system.  Here's the shocker - Ubuntu came up almost
flawlessly, despite the changed motherboard (as well as a different
video card, due to compatibility issues, though both were made by
Radeon).  There was just one problem - though the onboard LAN port says
it's working, it won't communicate.  I know that the ABit board used a
via-rhine driver and the Soyo used a rhinefet, but Ubuntu thinks it's
still got a via-rhine in it.  That's not surprising, due to the
similarity between the two, because it doesn't quite work.  I know the
port works because I just installed Centos 4.3 on another partition and
that works OK.  So how can I force Ubuntu to redetect the ethernet
hardware from scratch?
Thanks,
Vaughn