Crome OS & OSX 10.2.8
And once you do it, you'll wonder why you bothered. By today's standards, a G4 is an outdated processor, and once you add in the emulation (not virtualization- big performance difference!) layer, it'll be downright painful.
I can't wait for the real Chrome OS to come our way, but for now, I would hesitate to suggest any non-developer go out of their way to try it out. If for no other reason, I would hate to see Google's image hurt by this release. Although a lot of us can see the glory of what this OS will become, the average user I predict will think it completely useless and may never return.
So, johnnybrick, I will ask you to not try this out on your old machine, for fear of total disappointment, and maybe even not on your gaming rig, for fear of disappointment, unless you are planning on dev work on the platform.
I repeat, is this whole thing some kind of sick Google joke?
If you need help intalling the OS with VirtualBox, have a look here: