[ubuntu] Cannot boot 12.04.1 iso from usb on Macbook Pro 5,3

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http://ubuntuforums.org – I've tried making a bootable usb stick with the 'usb-creator-gtk' program with the 2 isos: precise-desktop-amd64.iso: refit manages to boot this one, and I select "Try Ubuntu without installing", add the nomodeset option, but it fails to load X and goes to a command prompt. precise-desktop-amd64+mac.iso: refit won't even detect a bootable usb when I try this one, so I can't even get to a grub menu with this one. Anyone know how to fix this? (Hardware)