I think this task is a bit more complicated than what you think, that is my impression from reading this thread.
First off, the distribution amplifiers will not be able to split the signal in parts of the frame, only clone what comes in.
Same goes for the switcher, it can switch between two inputs, and then what goes in, comes out four times.
So in other words, you need to get the four outputs from your computer, for this you have the 8400GS and a triplehead, this can give you 4 outputs, but if you want the 3 outputs from the triplehead to be fullHD it can only do that at 50Hz, so you need to check that whatever is receiving the signals can handle a 50Hz input, which it may or may not and you need the latest firmware of the digital edition and you need a dual link DVI output on the GPU and a short high quality DVI cable between GPU and triplehead.
So now, seen from your computer, you have 4 outputs, one seen from the computer as 5760 by 1080 and the other as 1920 by 1080.
If you have XP on the machine, spanmode exist, but it will only work with screens that have the same resolution, which these do not. So you need to run it with separate renderers, one for the triplehead output and one for the other output.
This means that you can not just out of the box use the conventional filestream node since it will not display its video over more devices (outputs) so using the filestream node you would need to synchronize two of them, each running 3/4ths and 1/4th of the video. or alternatively 4 streams each running 1/4th of the video
You can also use the vlc plugin that should be able to do the trick for you. I have yet to test it out for myself, but it should work.
When reading the specs of the machine running this setup, I am wondering a bit if it will be fast enough to play all this, you have an i3 processor with a 8400GS GPU, this sounds low end to me. Besides that, what is the speed of the harddrive? perhaps SSD is needed?. 4 times fullHD is quite a bit of data to shift around.
In any case you should definitely patch this setup on the hardware you will end up using, since there are quite a lot of parameters, both in hardware and software that need to be setup correctly that just sending a patch to others is asking for trouble.