Boot from a separate external partition?

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http://www.linuxquestions.org – I have a 320gb USB hard drive, one partition for my files, one for playing Wii games, and one which I would like to use for an Ubuntu instillation. To do this, I partitioned my disk accordingly using Windows, then booted from the Ubuntu CD to install the OS to my external hard drive partition. It asked me where I wanted to install the boot loader, so I selected the hard drive itself, rather than the specific partition, reasoning that it would scan the hard drive for a boot record. However, when I booted it (with USB boot selected) it simply said "No Operating System found, replace syste (HowTos)