How might I partition my hard drive so that I can boot Ubuntu from one partition and file storage in another. I am running Mac OSX Mountain Lion. I want to boot from my external Hard Drive into Ubuntu on a mac computer. My external Hard Drive is dual USB connected.
Appropriately partition your external drive. Create a Ubuntu live CD/USB and boot from it. When it prompts you to choose your install method, click
It will take you to a menu to choose the disk you want to install on. Choose your external drive, and create one partition that is >= the amount of physical RAM you have installed in your Mac, and format it as
Select the ext4 partition, and click install. Ubuntu will install on the selected partition. Follow prompts to set up your user account, password, and basically general things.
After Ubuntu is installed, it will prompt for reboot. Reboot, and as your Mac starts back up, hold the option/alt key and it will open up the boot menu. Select your hard drive partition, and boot into Ubuntu.