kindle, i got the same problem here.
my pc (i dont use it just for mining):
msi big bang xpower
2 x 5970
windows 7 64
I've tried to mine without enabling crossfire, but i failed.
i simply cannot make the 2 cards mine ate same time.
after a few tries (change positions of the cards, reinstall the driver with only one card and then insert the other, changing video cables, etc.), i chickened and stopped to try after i got BSOD and had to use the win7 disc to repair the Win 7 initialisation... i dont want to format this pc.
so i gave up and start mining with crossfire on. 1.2 GHs/s @ 840 MHz core clock and 300 MHz mem clock - 68C temp.
one thing thats still bothers me is the 50% cpu usage when im mining...
if you make your rig work without crossfire, please tell me how