It will work fine in your board.
PCIE is forwards and backwards compatible between 1.0 and 2.0, it auto negotiates for the fastest speed so it will work fine.
Any single card will work in that board fine, they only list which dual card setups they support because they require licensing so some only support CF, some only support SLI, some neither and some both, but if you only plan to run the single card you dont have to worry about it.
Thanks Hunter, I was a little concerned. I spent about $400 on a new build and forgot about the graphics card. DUH! I'm not much of a gamer. I'm working on a video workstation for my business. I will purchase a better card or cards later on to utilize the crossfire X. My old computer took a dump and I need to get this one built and running. Things are piling up quickly.