You should match the frequency (speed: 800MHz), latencies (e.g. 5-5-5-18), and voltage (e.g. 2.1V). If you cannot exactly match the first set's specs.:
-- Before you add the new sticks, leave your existing RAM in the board.
-- Enter the BIOS RAM settings.
-- Change the RAM settings to the higher latencies and voltages of the two sets of RAM (should be on on stickers on the RAM sticks).
-- Save and exit the BIOS.
-- Shut-down the computer, disconnect the power cord.
-- Open the case and insert the new RAM sticks.
-- Close the case, re-connect the power cord, and power-on the system.
You computer should now POST and boot into your OS.
-- Do not try to OC the computer unless each RAM stick has exactly the same specs.
Thanks for that, I appreciate step-by-step instructions. Overclocking is not in scope, but thanks for the advice.