AMD motherboards do not support DDR3 memory at this moment in time. But that is no real disadvantage as DDR3 isn't any faster than DDR2 because of the FSB limits:
http://www.xbitlabs.com/articles/memory/display/ddr3.html
As for which processor to choose, If you want the Phenom, then wait for the B3 stepping 9850 X4 which will have higher clock speeds and will cost around the same as the Q6600. It should be out by mid-april As to whether to buy the Q6600 or a Phenom. There isn't much of a performance difference between the 9850 and the Core 2 Quad so it's just a personal preference.