Check /etc/modules.conf and make sure this is there:
alias eth0 8139too
If it still doesnt want to load the mii module first for some reason add:
pre-install 8139too mii
then do: modprobe eth0
and post the exact error message.
Look in /var/log/messages for any errors referring to your nic and post them. It almost sounds like the nic is not being recognized by the kernel. Check the output of:
See if an IRQ is being assigned to it or possibly if the IRQ it is on is being shared with another device. Maybe the other device is blocking the nic from being seen.