I just bought an ASUS P8H61-M LX motherboard. This motherboard comes with a Windows driver package to enable the onboard ethernet port. My troubles with this board are documented here and here. After installing Windows the LAN did not work either, but after installing the supplied driver disk in Windows the LAN was then enabled.
I have been googling for the Linux driver but cannot find it. I see that others have used this motherboard in Linux, so apparently it is possible. I wrote to ASUS but I do not expect a reply for 48-72 hours.