hey farcaller,
I followed the comments of this thread to find a solution, but can you briefly sum up (in some steps), what you exactly have done to get the nvinject drivers working? Maybe we could even add this issue to the wiki, if zephyroth agrees, that it might be helpful.
That would be very nice, thanks.

Here it goes.
1.1.1. Get GraphicsUpdate, unpack it with pacifist and fix cpuid with Marvin's AMD Utility
1.1.2. Manually copy all the updates to root.
or
1.2.1. Get GraphicsUpdate, get patches.zip from this thread. Unpack patches to root (/) and install GraphicsUpdate. For me this results in lockup after install, but if you can reboot - do that.
1.2.2. Boot with -s (single mode), mount root as noted on the screen.
1.2.3. cd /patches
1.2.4. ./patcher cpuid-graphics.txt

2. At this point you'd better boot into -s (or continue old session), remove extensions cache and reboot with -f -v
3. If you get a lockup - you have to reboot in -s again and fix PCI IDs in corresponding kexts by the means of nano, vim or any other console editor. Remove cache, rebuild, boot with -f -v
4. If you get black screen at this point - back to single mode and try playing with NVCAP (found in the Info.plist of NVinject). You can get some here: http://nvinject.free.fr/forums/viewtopic.php?t=19 (04000100 00000300 0c000000 00000007 00000000 works for me).

I've tried your guide farcaller, thanks so far. But I couldn't manage it to get it workin'

I feel helpless, do you have any idea what I have done wrong? Or what else can be responsable for this issue?
I think maybe I should post on the NVinject forums, it seems, that my NVCAP key is wrong.