I installed Debian 8.4.0 PowerPC onto an iMac G5. When I tried using Debian, I only saw a command-line interface. startx didn't start the GUI. I did see an error message when I tried using startx, but it went away too quickly for me to read. This is the name of the install cd I used: debian-8.4.0-powerpc-kde-CD-1.iso.
What I expected was KDE to appear on startup. This is my Mac: http://www.everymac.com/systems/apple/imac/specs/imac_g5_2.0_17.html