device alias for an external DVD drive

[edward]

Hi,
I'm having a hard time booting a FreeBSD ppc 7.0 install DVD from an 
external firewire DVD drive on a PowerBook Titanium (G4/667).
I understand the open firmware device alias for an external firewire 
disk drive should be :
fw/node/sbp-2/disk_at_0:X
What would be the device alias for an external firewire DVD drive (I 
actually have both an external fw disk drive wherre FreeBSD should be 
installed and an external fw DVD drive from which to install from) ?
devalias doesn't seem to list anything that looks like it.
Thanks,
Edward