Enable booting from USB on Macbook with out OS X???

[ii bk ll]

I have a macbook 2nd gen with just Ubuntu installed on it. I am trying to figure out if its possible to boot from a USB HD. I installed OS X 10.5 on an external hard drive but i know booting from a USB is hard to do on a macbook with OS X so i am assuming that its near impossible to get my macbook to boot from a usb with just Ubuntu](*,). I am not sure if i am completely correct but i could not find any thing about macbooks with just Ubuntu on them. Is rEFIT an option or am i out of luck??:confused:

Any replies would be greatly appreciated!!!!

[cyberdork33]

Linux does not boot from external drives on a Intel Mac.

OS X should install to an external drive and boot without much issue.