Possible Duplicate:
How do I get my Mac to boot from an Ubuntu USB key?
I followed the instructions on Ubuntu.com to install Ubuntu onto a USB for a Mac. When I insert my USB in Mac OS X it now says The disk you inserted was not readable by this computer. Is this normal?
Also, when I start my Mac and press Alt the USB doesn't show up.
Does anyone know what I could've done wrong? I made the USB with the latest Macbook Air and am running it on a 2 year old Macbook.