As long as it's not a server board you wont need ECC memory. Do you have a mobo brand, model number and chipset identifier? Basically putting slower DDR2 memory, ie 533 into a board that takes 667 might cause a performance hit. It depends on your CPU and compatible front side bus speed. Ideally you want the same bandwidth from your memory as your CPU will handle. Without checking you mobo specs, CPU specs, and going to the manufacturers website that's about the best I can tell you.