according to System Profiler i have no built in audio and no pci cards.
I downloaded DPCI Manager and it shows both my built in sound device (Sis - 1039:7012) and my Sound Blaster Audigy PCI Card (SB Audigy - 1102:0007)

I've found and opened the info.plist for the apple ac97 driver, what do i need to do now to get my onboard sound working???

Refer to this:

http://forum.insanelymac.com/index.php?showtopic=119506

try entering device id ect pm if it work i don't have the time to try it on mine