2x2 + 2x1 dual channel

Since all your memory has to operate at the same voltage and timing, you are better off matching the memory. At a minimum, match memory in the same colored slots.

Your BIOS will run at the slowest timing so your worst memory determines the speed that all the memory runs at. You might see a message stating that "memory is operating in Flex Memory Mode".

"Intel Flex Memory Technology offers greater flexibility to upgrade by allowing different memory sizes to be populated and remain in Dual Channel mode/performance."

Bottom line is that it will *probably* work but you may have to play with the voltages to find an optimal setting. However, the term crap shoot also comes to mind so matched memory in all four slots is preferred.

Lower memory timing is more important than memory cycle rate. Get the lowest timing that you can afford. Also, 2.3v is at the upper end of the voltage range for DDR2. While your mobo supports up to 2.5v, memory specified as requiring less voltage will put less stress on the overall system. DRR2 was designed to run at 1.8v.

Thanks for the answers guys. So what I understand is there is no strict restriction about the second set. Just to make sure, I will be getting the g. skill ddr2 1066mhz (2x2) set, will I be fine with those?