trying to build this app has been a great opportunity to learn things for me. I make a lot of trial and error before posting here, and little by little things start making some sense.
about the display: I am working in a macbook pro (June 2010) with the discrete and integrated GPUs (one at a time, of course).
I will be hackintoshing a PC next month with a GTX295, then I will be able to try two GPUs at once (GTX295 = 2x GTX260).
but for now I will stick to my macbook.