Any ATI card above the X800 is crossfire capable (x800,x850,x1600,x1800,x1900,x1950,etc.). All you have to do is find the Crossfire-Edition card that goes with it.
x1900xt + x1900 Crossfire Edition
And yes, your board will run two DX10 cards in crossfire.
So wait, I need one normal card, and then
a CrossFire Edition card of the same product to go with it? Or two exact same CF Edition cards?