Can't boot on DVD to install

[edward]

Hi,
I dowloaded and burned 7.0-20051105-SNAP-powerpc-disc1.iso and tried an 
install on a PowerBook G4 667. I use an external DVD drive connected via 
firewire. FreeBSD is to be installed on a 5 GB partition on an external 
firewire disk, with another available partition for swap on the same 
disk. I have an external USB keyboard + mouse.
With the FreeBSD DVD in the external drive, I booted into open firmware 
and typed :
boot cd:,\boot\loader cd:0
I get :
can't OPEN: cd:,\boot\loader
Any idea what is going wrong ?
Thanks guys,
Edward