You pasted the same link as the MoBo instead of the graphics card you're wanting to get. I'm going to go ahead and guess its a recent video card (At least 1.7" in width) and say no it will not fit three. I can't determine just how far apart those PCI slots are but just looking at it they look about an inch apart. Also that is not a good MoBo to have three graphics card on. If all three slots are populated, only one will be x16, one will be x8, and the last one will be x4. A graphics card in a x4 slot is not a happy card.
You should be able to use two cards just dandy on that board, but it will not hold three. To address the PSU issue, 650W is enough for xfire 6850's. Read here for more details on that: http://www.guru3d.com/article/radeon...firex-review/4