I've set up bootable external hard drives at least 100 times or more. Recently I purchased a Mac Mini and a Alum Macbook Late 2008, I had a WD 500GB portable passport that had two interfaces (USB/Firewire 800). The portable drive was set up with four partitions, Leopard Installer, Leopard Server Installer, Intel Leopard OS, and Back Up. The drive had a partition scheme GUID which works best with Intel macs. Now here's the hickup, I managed to use this drive to install and troubleshoot Leopard on tons of different models. The weird thing is that when I tried to re-image my new Mac Mini with the drive via USB cable it would see the partition but fail to boot from it, but I was able to boot from the Intel Leopard OS partition with no issues. Now I read up on WD drives, other techs on apple's discussion board have mentioned that WD protable drives don't have the ability to boot macs and run into multiple issues. So I took the 2.5 drive out of the WD enclosure and place it in my own, then tried a second attempt but no success on booting the Leopard installer partition. I grabbed another portable drive, set it up from scratch with the same layout but still no luck. This gave me the assumption that my Mac Mini may have a logicboard issue of some kind so I tried using both portable drives on my Alum Macbook and got the same result; it can only boot off the Intel Leopard OS. Both Macs have the lastest firmware installed which really shouldn't prevent me from booting off the image of a Leopard Retail disc but each mac can boot off their on installation dvds that came in the box, and a homemade clone of a retail copy of Leopard. The Alum Macbook I have is the one that was release without firewire, so booting off of that isn't and option, furthermore, they don't have the ability to start up in target disc mode. So even though my Macbook is somewhat handicap, I figured my Mac Mini should be able to follow through because it wasn't design with these faults, yet my hands are still tied in a knot. I know I'm not crazy but let me know if you ran into a similar issue or have a solution to the hell I'm experience from what you read above .