Thank's a lot spylinux.

This is a great hope for those having an AGP video board and willing to jump into Snow Leo.

Here is my story.....
I run 3 hackintoshes with AMD CPU and Nvidia Geforce 7600 GS AGP.
I successfully installed
10.4.9
Tiger
Leopard
More details on my conf:
MoBo AM2NF3-VSTA chipset nForce3 250, Audio CM6501
GeForce 7600GS 256 Mo
AMD AthlonX2
2Go DDR2
SATA 500 Go (running 10.4.9, Tiger, Leopard)
SATA 160 Go (running chameleon 2.0, Leopard 10.5.7, SL 10.6.1)
but Snow Leo failed, I was always stuck with frozen video resolution and no QE/CI.
I tryed DSDT, posted question to specialist about my 7600 GS AGP, they drop my demand to basket
others wrote ( and you can find it on several forums) AGP don't work with SL
no way, don't loose you time ! that's wrong.

Until last evening, I was searching without much hope.... you never know!
and your ATY_Init.kext did a tilt! I did not know this one, let'us try.

And it works ! wooooooh !

What do you need really ?
What I did and works for me:
1) Put ATY_Init.kext in my /Extra/Extensions
2) Mount SL image on a Leopard partition, and from System/Extensions, copy on my desk
GeForce.kext *
GeForce7xxxGLDriver.bundle
GeForce8xxxGLDriver.bundle
GeForceGA.plugin
GeForceVADriver.bundle
NVDANV40Hal.kext *
NVDANV50Hal.kext *
NVDAResman.kext *

I search into info.plist and insert my video board ID 0x02e110de where
it must be: .kext with a *: first and three last above.
Then I put all the .kext in /System/Library/Extensions/ replacing previous if necessary.
3) fix permissions in /Extra/Extensions and in /System/Library/Extensions/
Rebuilt 2 extensions.mkext
Put the second one in the right place (system/library/caches/com.apple.kext.caches/Startup)
4) Add GFX string (Osx tools/ video GeForce 7600 GS 256 Mo) com.apple.Boot.plist
5) remove any DSDT.aml if any
6) reboot now on your SL partition and your GP is now seen as PCIe board in about this Mac.
In system preferences all screen savers works fluently.....

great job

Thank's again spylinux.