Here's some wonderful sketches of the Macintosh interface evolution that span back to the Lisa prototypes. Those system 6 and 7 screen shots get me all misty-eyed...I used to live and breathe Macintosh in those days. Funny that the Lisa had multitasking and protected memory in 1984, I wonder how that was left out of the Mac? Really, back in 1984, it wasn't needed in a personal computer. Grafting a user interface onto a free version of Unix probably wouldn't struck them as pretty damn strange back then.
Thanks to Ben for the link.