i myself am running a Giga-byte GA-7n400 Pro motherboard with the Nforce2 ultra-400 chipset. It also has the nForce2 AC97 Audio Controller onboard. There only one place you need to go to fix your sound www.nvidia.com.
Go into their download section and there is a system driver(sound and lan) for nforce and nforce2 chipsets running linux. They have a great readme that helps a lot if you actually read it. Oh yeah, and don't expect to be able to have multiple programs accessing the sound card at once. The drivers work but you can only do 1 thing at a time. This is why i tossed the old SB LIVE back into my system and disabled my nforce2 audio.
HOPE THAT HELPS