X1800 XT Crossfire may require 800w
As you have probably read in the reviews, the new ATI X1000 series require a lot of power. We’ve learned that the X1800XT is a power pig, it can use up to 270w at full load. A typical AMD64 based system requires around 200w in a good case scenario. Two X1800XT cards in Crossfire could demand up to 540w, add this to a normal system power requirement and it could easily reach 740w or more if you use any extra devices.
If you are planning to go with Crossfire and two X1800XT cards, make sure you get a really good power supply. I doubt if there are many 800w power supplies on the market yet but if we know the power supply manufactures, it shouldn’t take long for them to arrive.