Try this command :
grep CONFIG_TIGON3 /boot/config-`uname -r`
If you see «# CONFIG_TIGON3 is not set», you could try to recompile a custom kernel, just with that option changed. It is the driver for a Broadcom Gigabit card, and your motherboard include such a controller.
If you have a /usr/src/linux, you just have to do that :
cd /usr/src/linux
cp /boot/config-`uname -r` ./.config
make xconfig
Then go in «Networking device suppor», «Ethernet (1000 Mbit)» and click on the «m» of the Broadcom card. Then save and exit, and run :
make dep && make bzImage && make install
Verify in the Kernel-HOWTO, I'm not sure anymore (I'm using Debian, and it's own kernel building system).
http://www.tldp.org/HOWTO/Kernel-HOWTO
You just have to add a line with :
tg3
in your /etc/modules, or run :
modprobe tg3
to have your controller working.