Hello!
This weekend, I created the first usable installation image for ppc64:
https://people.debian.org/~glaubitz/debian-cd/current/
It should install fine on any 64-bit-capable PowerPC (e.g. Mac G5).
When asked for a mirror during installation, enter:
* Host: http://ftp.ports.debian.org
* Directory: debian-ports/
Cheers,
Adrian
--
.''`. John Paul Adrian Glaubitz
: :' : Debian Developer - glaubitz@debian.org
`. `' Freie Universitaet Berlin - glaubitz@physik.fu-berlin.de
`- GPG: 62FF 8A75 84E0 2956 9546 0006 7426 3B37 F5B5 F913