Well, sorry to report it. Every Debian for PowerPC crashes on 64-bit G5 Macs. Work prevents helping but here's screen output.
Kathy
found display : ...
copying OF device tree
Building dt strings ...
Building dt structure ...
Device tree strings ...
Device tree struct ...
Calling quiesce ...
returning from prom_init
Invalid memory access at
% SRR0 00000000.01403900
% SRR1 10000000.00083030