I just received my new Seagate Momentus 5400.6 (500GB) drive in the mail today, I went to install it in my machine, once I installed it the MacBook doesn't recognize it in system profiler or disk utility. I removed it, but my old 5400rpm 250GB WD back in and put the new 500GB seagate into an external enclosure and there was no problems. The MacBook recognizes both drives simultaneously this way. Is there any reason why when I boot the machine with the 500GB internally and the 250GB in the enclosure it only sees the 250GB but when I attach the 500GB externally and the 250GB internally the machine sees both? I do realize that the 500GB drive is sata 3.0 and my MacBook is sata 1.5 (I have the Late 2006 MacBook) so I also tried setting the jumper on the 500GB drive to perform only at sata 1.5... it made no difference. If anyone has any idea why this is happening please let me know, it'd be greatly appreciated.