I installed Ubuntu on a USB drive. I'm trying to start it from a Mac. rEFIt sees it, but when it tries to start it, it starts Windows on the main instead. I tried to start it from the bootable disc Super Grub2, but when I start Grub on it, Grub can't see my USB drive at all.
Is there anything I can do? I can boot from a CD and once I'm inside of Grub, I should be able to find any drive and boot from it, right?