yaboot and usb volumes --

[info by mac-conf]

Hello all,

does anyone here can support me as install yaboot files, to boot an  
USB volume. I would like to start directly my usb volume with ubuntu  
when restart the machine and press <option> button. I can see the  
linux logo with snapshot volume, but when pressed then, the system  
still show me the same splash screen image with all volumes bootable.

thanks in advance
marco