Ddr2 or ddr3 ram?

No you cannot, the notch in the sticks is in a different place to keep you from putting DDR3 chips in a DDR2 board. The memory controllers and voltages are different so it wouldnt work properly.

Right^ DDR2 and DDR3 aren't compatible, even if they were,i wouldn't recommend going from DDR2 to DDR3,(with the same capacity),because the performance difference isn't much.