[ubuntu-in] UNR on macbookpro 5,1

[Linux Lingam]

i've got it to work somehow.
the technique is to hold down the option key on boot-up, while keeping
the usb-thumbdrive connected.
the screen changes to show two options:'rEFIt' and 'Windows'. [note
the lack of macosx, or even mention of linux on my partition, and the
inaccuracy of naming my linux partition as windows]
click on 'rEFIt'.
it opens in turn to reveal three choices: macOS, Linux, and the usb-thumbdrive.

when i click on the thumbdrive though, it does not boot into UNR.
the system displays an error to the effect the thumbdrive does not
have a bootable OS installed,
which is incorrect, since the thumbdrive has a live version of UNR.

anybody with a macbookpro, please try and share your experiences.
thanks

regards
niyam