I have a first generation Mac Pro 2.66 ... it has 3 gigs of RAM, and I want to add four more to it. Right now I have two 1GB chips in the first two A riser slots, and two 512mb chips in the first two B riser slots. (The very first 1GB chips is showing ECC errors, but OWC is sending me a new pair to replace it.) If I have two 2 GB chips coming from OWC, how should I fill the slots? Thanks!