@stickygreen : i've search for Roku but i cannot figure how to play extended 5x1 video with that without an expensive system. The digital signage solutions are way over my budget.
It's going to cost less in the end, trust me, this is what i specialize in. Fixed/permanent and mobile/temporary video instillation, projectors, monitors, TV's, multi-screen, video mapping, edge blending, even full dome content and live playback.
I don't come to this site cause I'm a gamer...
The system that you've spec'd out, isn't very powerful, and could cause you issues in a few ways. It's really hard to understand exactly what you are trying to do, because you haven't explained it in detail. I can tell you, that running 12 monitors at XGA resolution will take a much more powerful system than what you're planning to use.
If you'd like to get into more detail i can help. I will need to know.
total number of images to be shown - how many have to be spanned content, and how many are single displays, can any of them be the same image, like the LCD monitors in the corner of the room?
types of displays - resolution, input connection type.
cable lengths, and type?
your expectation for length of video clips to run, and is this on a loop, or do you want to control it?
your expectation of resolution, codec, file format?
and most importantly, your expected budget?