Hello everyone, I just purchased a 4 gb kit of ddrII 800 (PC2-6400) for my previous generation 15" MacBook Pro (2.6 ghz Intel Core 2 Duo). I know it only supports ddrII 667 (PC2-5300) but was under the assumption that it will down clock the 800 to 667 speed. However, my laptop will not even boot with them in. I know the modules are fine because I loaded them in a 24" 3.06 ghz iMac which supports ddrII 800 and it boots just fine. My question is, was I wrong about it using them at 667 speed and it will just not use them at all. Any replies from anybody with experience on this would be greatly appreciated.