Yep..thats Mac OS X running there…
Macboy modder (flickr user Charles Mangin) dug out his old Mac Plus, disemboweled it and crammed the innards of a modern Mac G4 Cube inside including replacing the old B&W screen with a nice shiny LCD. He even spooned out the guts of the old Mac mouse and replaced it with a modern optical USB version.
Now i would like the inards of my PS3 stuffed in an Amiga 500+ please!
For the full picture set, visit his flickr page here and here. via