How can I make a bootable USB ubuntu live disk for a Mac using Ubuntu?

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http://askubuntu.com – I've found guides that explain how to make a bootable disk for macs using macs, but I want to use ubuntu to make this mac-bootable disk. Is there a way to do that? In other words, I have: a laptop that runs only ubuntu a 4GB usb thumb drive a Mac Mini 5,1 with non-working OSX Lion and I'd like to install ubuntu on the Mac Mini. I tried following the instructions here: http://studyblast.wordpress.com/2011/08/14/guide-mac-os-x-lion-how-to-bo... but the mediafire download that this guide requires is no longer avail (HowTos)