Hi there, I received my new i5 MBP today. After booting it once with the installed HDD to check if it's ok, I exchanged the hard disk for the one in my Late 2008 Macbook Pro. After doing this, my Late 2008 Macbook Pro boots fine with the (new) hard disk from the new i5 MBP, but the i5 MBP does not boot with my old hard disk. To give you some details: - I have installed 10.6.3 on the (old) hard disk that's not booting. - The i5 MBP boots fine from the installation DVD - Disk utility finds and can read my hard disk, no errors - PRAM NVRAM reset did not help - when booting in safe mode, I can see the system stop booting after or while loading Extensions.mkext My guess is, it tries to boot and load the wrong Extensions for the new system (CPU? GPU?). I have no idea how to fix this. Solution: Re-install Mac OS X from the installation DVD that came with the i5 on top of the existing (old) system. This takes around 45min. and leaves your data intact, but adds the Core i5/i7 support. Any help would be greatly appreciated!