You said your getting a blank screen? It might be something other than the graphics card? Have you ever been able to boot into Leopard without
editing the info.plist's? If so than good, I have the same card as you and this is what I did to get full hardware support with the 8600gt.

Go through all the steps in this tutorial, Ive got the same card as you.

http://forum.insanelymac.com/index.php?showtopic=53052&hl=geforce%208x00&st=148 0

This is what I did, downloaded all the files it asks for, including the new NVinject 0.2.0

edited all the files it ask to edit in step three
I also edited NVDANV40hal.kext and added the device id there as well because someone told me to do so also.

after going through all the other steps in that link, editing all the files is asks to edit, including the NVDANV40hal.kext, mine works great.
I have full CI/QE support!
Unfortunatly, to get the full 512mgs of ram, it looks like we need to flash our cards which could actually fry them if something goes wrong, so Im happy with full support with only 256mgs.

Hope all goes well.