Hello,
 
I recommend that you try using DSDT for fixes becuase you need less kexts and editing
 
http://www.insanelymac.com/forum/ind...=#entry1547148
 
you can also make a dsdt edit so that your 7600gs devide id in gfx0 is the same as the 7600gt pcie in the imac. This means you would not need to edit the nv kexts at all.
 
http://www.techdc.com/imac-24-opened-and-upgraded
 
DSDT works as PCI on AGP, but it looks like i was one of the only people that have done this.
 
dsdt edit should be done at the place when your 7600gs is located in ioregistry explorer.
 
The original postion in my example was VGAB within the AGPB device
 
pcj also has a fix and he uses some extra strings from the PCIE cards. However, i am not sure if they are needed. The example i gave worked fine on leopard
 
pcj's link is here if you need it
 
http://www.insanelymac.com/forum/ind...threaded&start=
 
Do further research if necessary and good luck!
 
You could also try using the bootcamp vga rom from the imac as well and edit the clocks to match your own card in nbitor. howver, it is up to you how far you go with this.
 
you can get it from here 
http://support.apple.com/kb/DL978
 
However, you will need a hexeditor to strip the efi section from the rom and nbitor to edit the clocks etc. 
 
the .efi parts you want are located in the package
 
Too busy right now to write any more. Reply to message for questions
 
thanks,
 
lemonsoda
 
ps, i have been told that nv4 kext does not work on 64bit mode (arch=x86_64) after 10.6.2
 
this is shared by 6xxx and 7xxx nvidia cards. However, I never tested this