I had 2gb od ram (dual chanell) and I have recently bought 2gb more of the same memory (Corsair Dominator 1066mhz 5-5-5-15). While 2 gb are working properly even overclocked, 4gb cause blue screen when they ran at 1066 mhz. I tried to increase the voltage to 2.2 but it doesn't help. My system is stable only when I drop the speed to 850 mhz. I have Vista 64 bit, Gigabyte p35-dq6 and core2duo e6850. PS. My problem is similar to the Camnipoten t's - he also had to decrease the speed of ram and found no other solution.