Did you do this from a clean install? (No other graphic drivers present). If you notice, in every method it says this is a must.
IE:
"Step 1: Use a FRESH install for best results. With a current install it still might work, but mods might mess up the process, and previous driver installations might make this not work."
He could actually change that 'might' to WILL.
"...prior to making these changes, browse over to /system/library/extensions and delete NVinject/Natit/NVKush.kext or whatever you were using and reboot."
Ditto EFIStudio or anything else. Also, take note, from the Aquamac guide:
"One more thing, if you have a 512 card or a 768 mb card as I do, you have to insert Total ram size int your in.plist file with XML editor just like in nvinject.
EDIT: I have now included pre patched templates for a number of 512 mb, 768 mb & 1024 mb cards at the start of the post so you do not have to change the vram size."
So EFIStudio and many other methods will not work with your specific 768MB card- it needs a very specific hack to work correctly.
EACH time you try a driver method of some sort and it doesn't work- you need to get rid of any changes the previous attempt may have made to either kext files, or the boot.plist. The problem with that is, you may not know what all has been changed in your Extensions folder. I know it's a PITA, but because of that, I'd highly recommend starting over from scratch.
If you really want to do things methodically, and absolutely correctly- then here's what I'd advise you to do:
Create TWO Mac OSX partitions on the same drive. Install Mac OSX to BOTH. DO NOT install any graphic drivers in either partition.
Boot into one, and open the System/Library/Extensions folder of the other, and apply a color label to EVERY file in the folder. You can't do this (easily) to the same partition you're booted in due to permissions issues. Boot the other system, and apply the same to the other.
Now try the hack methods. Keep a backup copy of your working com.apple.boot.plist. If anything like nVinject adds kext files to the extensions folder, all you need to do is look in the folder and see what doesn't have a label, it'll stand out like a sore thumb. If a driver doesn't work, you know you can delete it, and try something else. Also- because you have TWO working installs of Mac OSX, if just in case during your trials with a driver you completely bork something (It CAN happen quite easily) you merely can reboot into the other install, and fix the other- again by merely removing any unlabled kexts that fuxed the other system up.
I can't recommend this method enough if you're going to go Hackintosh.
It'll cost you roughly 7-10GB of disk space and the extra time spent installing OSX twice rather than once.
It'll save you UNTOLD hours and handfuls of ripped out hair if if/WHEN something goes haywire or needs to be messed with like you're experiencing with your graphic card.