networking hosed after upgrading to 10.04

[scar]

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i finally decided to upgrade an old machine from 9.10 to 10.04, and
there is something strange going on with the networking.

this machine is only connected to my LAN using one ethernet port, and i
also had previously set up a bridge for use with a virtual machine i
have installed, so a rather simple setup but not standard.  i just used
the KVM setup guide on ubuntu.com somewhere to setup the bridge.

when the system boots up, it can't be found on the LAN, and it can't
connect to websites either.

in network manager i have several different connections that i don't
remember having:

Wired connection 1
Auto eth0
Auto Ethernet
ifupdown (eth0)
ifupdown (br0)

i'm pretty sure 'auto ethernet' was the only one i used before.  it
seems after i pick any one of these to connect to, i then have access to
my LAN, but still can't reach any outside websites for example.

also, when i was running 9.10 my motherboard blew out and i had it
replaced under warranty.  however, a different model was sent since the
original had been discontinued.  i remember something strange happened
with the networking at that time too, but i was able to get it working
with some help from my loco team, and haven't had to fuss with it since.

it seems to me this chain of events may have really messed up my
networking (this system has been upgraded since 8.10 too).  i'm
wondering if there is a simple way to wipe the slate clean and get my
LAN and bridge connections configured again...

thanks
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