After some tries i have solved the problem for the output on the DVI (digital) on the 8400 GS
In the first time i tried only with VGA (analog) but the quality of images was absolutely not good.
So after some research on this forum i have tried to activate both outputs (DVI VGA) and now the DVI output work very fine.
Attached the modified NVINJECT.KEXT for activate both outputs (DVI VGA)
Change, repair the permissions (CHMOD CHOWN), reset extensions.mkext (KEXTCACHE -K) and reboot