The "NF4" in the name means it's a Nvidia NForce4 chipset on the board, and
this page confirms this. I have a different board with the same configuration (AMD Socket 939 & NForce4), so you'd need to get the NVidia Forceware drivers. Select "NForce", "NForce 4", then "NForce AMD" on the
drivers page.
Did it come with a CD? It's a big download (43.1MB). With reasonably new drivers, I've never had problems with that network port - it just works.