What about the rest of the components.? You need to provide info on the processor you are using and any overclock that you may have performed on it.. Do mention your budget also.. Meanwhile, a good 450W PSU (like the Corsair VX 450) is enough to power a single GTX 260.. Considering an overclocked processor and other standard components (hard drive(s), optical drive(s) etc.) a good 550W PSU should cut it..
As for the maximum consumption of the cards, Nvidia claims 236 W for the GTX 280 alone and 182 W for the GTX 260.
I believe this is for the original 192SP GTX260. For easy math and extra shaders (and PSU headroom) lets say 200W per card. Seeing as you'd need two of them for surround view, you'll need 400W just for the GPUs. And another 100W for the CPU and your at 500W. Another 50 or so for the mobo and other devices, and I wouldn't run anything less then a 550W. I personally would get a 650W or better so you don't stress the PSU to bad. One of those Antec, Corsair, or XFX 650W should be fine. Make sure it can do around 500W on the 12V rail.
The gtx260 can run two monitors. If you want a third monitor, you need an extra video controller. Possibly, your motherboard has an integrated controller, or you will need a second discrete video card.
They are built into the drivers. You download either AMD or Nvidias drivers and install them. (whichever you own of course.) Built into them now is the ability to use more then one display as one display. Setup is different for each one, and you need an SLI setup in Nvidia's case. Once you have it setup however your three monitors will show as one to windows or any games you have.