I'm running a Fedora 15 test image on an external USB sata drive. I formatted the drive as ext3 and copied the filesystem to it, and manually boot from ofc: boot u:\boot\olpc.fth (or something like that) You might have to tweak the olpc.fth file on your usb disk to boot properly off it, and don't forget to update your /etc/fstab to use the new drive devices.