LOL, that's funny, I've just got my 8400GS to work 2 days ago and, wouldn't you know it, it's a 0x10de10c3 also.
The funny part is that my 8400GS is a Gygabite 8400GS with 512MB DDR3 RAM and VGA/DVI/HDMI.
For me, to get it working, I had to enter my id into the GeForce, NVDANV50 and NVDResman kexts, install NVEnabler and have GraphicsEnabler set to Yes.
Now that it's working, I'm worried about removing NVEnabler to see if it'll work with only my modified kexts and GraphicsEnabler.
EDIT:
Nope, doesn't work without NVEnabler... I've even got the PCIRootUID in com.apple.boot.plist, but no dice.
EDIT2:
Just to clarify, I've got a dual screen set-up with one screen on VGA and the other one on HDMI. Unfortunately, when I use DVI and HDMI, I get picture on only one monitor so I have to have at least one of them on VGA.