I found a number of people facing problems configuring their NIC card for ASUS P4P 800SE Motherboard. I managed to solve it (because I faced the same problem before). Here I included the steps needed, which I copied from the installation manual:

To compile the driver, go to the directory /usr/src/linux and
execute the command "make menuconfig" or "make xconfig" and proceed as
follows:

To integrate the driver permanently into the kernel, proceed as follows:

1. Select the menu "Network device support" and then "Ethernet(1000Mbit)"
2. Mark "Marvell Yukon Chipset / SysKonnect SK-98xx family support"
with (*)
3. Build a new kernel when the configuration of the above options is
finished.
4. Install the new kernel.
5. Reboot your system.

To use the driver as a module, proceed as follows:

1. Enable 'loadable module support' in the kernel.
2. For automatic driver start, enable the 'Kernel module loader'.
3. Select the menu "Network device support" and then "Ethernet(1000Mbit)"
4. Mark "Marvell Yukon Chipset / SysKonnect SK-98xx family support"
with (M)
5. Execute the command "make modules".
6. Execute the command "make modules_install".
The appropiate modules will be installed.
7. Reboot your system.

I downloaded the driver too from ASUS website, but I didn't use it at all. Please correct me if I were wrong.