You can use Uinstaller from Pcwizcomputer.com that will create the strings you need and put them in the com.apple.Boot.plist file for you.

Hope this helps

EDIT: My bad, just checked and it doesn't have your graphics string. Ithink you can copy the graphics string using a text editor or plisteditpro.

FYI, the file to be edited is located at /Library/Preferences/SystemConfiguration/com.apple.Boot.plist in both Leopard and Snow Leopar

I would also remove nvinject.kext from your extensions folder, then run "Kext Utility" to fix fix the permissions and create the extensions.mkext file

Edit 2: Adding the gfx string from leo probably doesn't apply in your case. Sorry for thinking I knew what I was talking about.

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System 1: Gigabyte GA-P35-DS4 MB with Intel e6750 Core 2 Duo w/8 GB RAM (Retail install)
GeForce 8800GT 512MB, Snow Leopard 10.6.2
System 2: Dell Optiplex GX280, Intel P4 3.0Ghz w/3GB RAM
GeForce 7800GTX 256 MB, Leopard 10.5.7 using iATKOS v.7 install (work in progress)