USB Flash drive with Ubuntu will not be recognized

[billilene]

HI dear people,

I've trying (2 days!) to install Ubuntu on a flash drive as bootable with no success...

My last try was:
-Download ubuntu-12.10-desktop-i386.iso
-Convert it to an .img using:
hdiutil convert -format Rdxx -o /path/ubuntuconverted /path/ubuntu.iso
-List the Disks and unmount the flash drive with:
diskutil unmountDisk /dev/diskN
-install ubuntu image with:
sudo dd if=/path/ubuntuconverted.img of=/dev/rdisk1 bs=1m

Then I got the message: "Medium can not be read, ignore, initialize or eject"

With another method, I got the same message, still tried to boot it with restart and alt, and the computer didn't show the Ubuntu and actually crashed and since this time, the restart are very slow. So this time, I prefer not to try...

I'm using MAC OSX 10.7.4 on a MacBookPro 8.2

Any idea what went wrong???

Thanks, Billilene