I tried the g3g4.iso on my TiBook (867mhz) and I got it to boot, I am posting this post from it (gnome).
I found that if I hold down the c key on bootup it will boot the cd and avoid the yaboot, if you have one installed. Because the yaboot will try to boot the cd (it will take a very long time to do it).
I used Xeasyconf with no problem.