You will need to set the existing RAM up first to match the higher timings (higher Cas) & lower voltage of your new RAM. This will help prevent issues once you install the new RAM.
Thanks for the reply. Not having adjusted memory timings before I assume I should do that when I first boot the new setup in the BIOS, correct? I would install the 2 GB kit that has the 4-4-4-12 2.1V (existing RAM) timings, adjust the timings and voltage, go through installing the OS (Windows 7 64-bit) and then install the new RAM sticks?