If you replace your network adapter with one that uses a different network driver, before rebooting the second time, rename the /etc/hostname.olddriver0 file as follows:
# mv /etc/hostname.olddriver0 /etc/hostname.newdriver0
Any time you add, remove, or replace hardware, run the Configuration Assistant utility.
After renaming the driver, perform a reconfiguration boot for your changes to take effect:
# touch /reconfigure # reboot