Harry, thanks very much for the reply. I tried your suggestions with mixed results.

Booting in expert mode and with the NOAPIC option didn't seem to make a difference.

When I used sudo mii-tool -r the first time, I got
eth0: no link
eth1: no autonegotiation, 10baseT-HD, link OK

So I plugged my DSL modem into eth1 and I was able to connect after running netcardconfig.

However, after I rebooted and did sudo mii-tool -r, I got the following output:

SIOCGMIIPHY on 'eth0' failed: Invalid argument
restarting autonegotiation...

Haven't been able to connect on knoppix since.

Both network cards show up during the startup chatter.

To answer your last question, I haven't installed any Microsoft updates, patches or software recently. The only updates that would have happened on the windows side would be the virus database (using AVG antivirus).

I still haven't tried removing the soundcard, but if nobody has any more suggestions I'll try that next.