If your board came with the optional on-board LAN card, you have a Silicon Integrated Systems [SiS] SiS900 10/100 Fast Ethernet card, this card is supported by Linux kernels 2.4 and later (that I know of, as I only use 2.4 kernels).
To make it work you should type
modprobe sis900
and you should see something like this in your syslog:
sis900.c: v1.08.02 11/30/2001
eth0: SiS 900 PCI Fast Ethernet at 0xd400, IRQ 5, 00:d0:09:ea:7a:98.
or type
dmesg | less and scroll to see the kernel messages.
If everything went fine, you may add sis900 to /etc/modules
so it will autoload everytime you boot:
echo "sis900" >> /etc/modules
(or echo "alias eth0 sis900" >> /etc/modutils/aliases && update-modules for the module to be loaded when needed, go for that if you have a Debian system)
Pay attention to the double >, or you will have troubles :]
or compile it in your kernel, where you should say Y to SiS 900/7016 PCI
Fast Ethernet Adapter support in your kernel
configuration.