[Macpartners] booting PowerMac G5 from external USB drive

[Felix Kreisel]

Hi,
I am trying to install Leopard from an external USB DVD-DL drive. This  
device, a LiteOn DX-20A3H rewriteable, drive does not show up on the  
list of bootable devices in either Preferences->Startup Disk or when  
booting with the Option key down.
I am tearing my hair out because I bought the LiteOn drive  
specifically to upgrade the Mac to Leopard. Can anyone suggest a  
solution?
Many thanks,
Felix