Re: multiple monitors
With the hardware that you want to use I can tell you that this would be damn near impossible. There is no way that I know of or even heard of to mix nvidia and ati cards. If you are willing to give up your hardware acceleration then that is a compleatelly diffent beast. In that can you can do that even though it is time consuming, oh yeah and you will need a third video card. The most elaborate setup that I have seen is a computer with 3 pci tnt2 cards and 1 agp tnt2 card. There were 4 monitors and 4 sets of keyboards and mice connected to the computer and you could run programs on all 4 terminals as if they were separate computer. The performance wasn't amazing but it was good enough so it's usable. Now keep in mind that that was a computer designed by HP and I believe it would soon be available for retail in Africa and some other 3rd world countries. HP has a lot of people very proficient in everything linux and unix related. So for you setting up your configuration might be a gigantic task (I have no idea how much you know about linux, your particular distribution, and your version of the X server).
So to sum all this up, if you really want to use 3 monitors in the way described look into buying a matrox card. anything else would most likelly be too hard for you to setup and you are not very likelly to find help with it for free.