GT780 with AMD graphics card

is the GT780 laptop that originally came with a GTX560M compatible with any AMD GPUs, specifically the HD5870M? I have one installed replacing the GTX560M thats broken and the laptop doesnt seem to pay nicely with it. The big issue is that Ive lost the ability to adjust screen brightness.


The GT780 is a bit different. It didn't have an 'integrated GPU' and a 'dedicated GPU' like the newer GT and GE series laptops do.
Because of this, the GT780 should work with an AMD/ATI card just fine to be perfectly honest.
The things you're 'having problems with' were particular to the NVidia card I believe, since it was actually controlled via SCM. This would have had to interface with the NVidia driver. Now that you're using an AMD/ATI card, SCM can't do the same things it did before because the hooks to work with the NVidia drivers won't work with the AMD/ATI drivers. For instance, the brightness probably won't work because of the settings it has to change. BUT I'm willing to bet if you use the FN+(whatever) keys to change brightness it will work.
The P1 button was a 'turbo mode' for the GPU, specifically for NVidia based cards. This will not work with an AMD based card.
The movie clip button probably changed the video profile being used in the GPU drivers and again, since you're not using the NVidia drivers anymore that button will no longer function.
Basically, what I'm trying to say is all the buttons you're having problems with had hooks that linked into the NVidia drivers and won't work with the AMD/ATI drivers.
If you aren't having issues with games and anything else, I'd just be happy that it works and you can play games.