Hi Folks, I bought a 320Gb external HDD which was to replace my internal 160Gb drive in my Unibody Macbook. I used SuperDuper! to copy my original disk on to the new one, then swapped the disks. My 160Gb is no loger working, which is fine, but I want to install a fresh OSX on to the new hard drive. I can use the Disk at the moment but the mac can't boot from it. I need to hold down the option key and select it at startup, I presume because of the format/partition type. When I try to do a fresh install of OSX, I get an error saying cannot install on this disk because of partition type (GUID Tables). I'm not allowed to do anything to this disk because I can't 'unmount' it, so, can I run disk utilities from my install DVD? before mounting the disk?