Those cards use tons of power when you first boot up the system. In fact, they use more power at start up than a 6800...then it goes to the normal ATI low-power usage.
Yeah, i'm sure that card will run it anyway. I have a 9800 Pro, and i'm sure it'd run it.
new cards will run any game anyway if you have the latest direct X version installed, and it'll only be the frames per second that will take a hit while your playing the game.
This can be fixed simply by lowering settings in options until the video card produces a suitable speed to play.
Though I'm sure you wont have this issue. You could probably run at reletively high settings, depending on the resolution you use