This problem with forcedeth module seem to affect all major Linux distributions. Year 2008 was the first time I reported this issue on a ubuntu bug tracking system. Just recently I have installed around 6 Linux distribution and in all of them my nVidia Corporation MCP55 Ethernet (rev a2) network card does not work and this includes latest fedora 13. The fix is still the same:
rmmod forcedeth modprobe forcedeth msi=0 msix=0
Ubuntu and Debian users can make this fix permanent with:
echo options forcedeth msi=0 msix=0 >> /etc/modprobe.d/options update-initramfs -u reboot