How many slots do you have? 2 mirrored bays? (4 slots) I'm not sure, but that is what I think all rdram boards are. Anyway, I'm assuming you'll still be able to use your 2 old 64 md sticks. Are they PC-600 or PC-800? If they arePC-800, you might as well get the same thing on the new ones. If they are PC-600, the PC-800 will just run at the slower speed.