ZBrush 2.03 for Mac, already activated.
Goes without saying because this version of ZBrush is so old, it's basically useless for commercial use, but I provide it for educational and historical preservation purposes only.
Look through the Images and ZTutorials folders, I think you'll get a kick out of this time machine.
I've only tested it in Leopard on a G5 quad 2.5 GHz, works great.
Available separately: version 1.x
CompatibilityPPC G5