Is the PC2-5300 DDR2 667MHz SODIMM (want to buy) backward compatible with PC2-4200 533 MHz (my notebook)?

Answer 1

If you mix it w/ a ddr2 533mhz, it will just run at that lower speed. If your motherboard supports only ddr2 533, the BIOS will read the SPD of the ddr2 667 and just automatically set the speed and timings as ddr2 533. If your laptop supports both ddr2 533 and 667, your new SODIMM should run at 667mhz.