Apple and Xerox
Apple did not "rip-off" the Macs UI from Xerox. Apple had hired some people from Xerox (like Jef Raskin, Bruce Horn) who believed in concepts of a Graphical User Interface. These concepts are pretty broad -- like making a computer easier to use by using graphics (icons), using menus, windows and making a consistent interface to do things. The work on these concepts predates Xerox PARC -- in fact it was many of these peoples individual work on those concepts that got them hired at PARC. So Xerox (PARC) brought them together to refine them.
Apple's work on GUI's predates Steve Jobs visit to Palo Alto Research Center. Apple had already had the same broad goals of offering an easier to use computer, and possibly using some of the same concept (like menus, icons, and graphics).
Remember the following: Icons were not new, we had been using them for years for international street signs and so on -- they were only new on computers. Menus were not new, text based menus were being used and had been for a while. Graphics weren't new, though how much they were relied upon was new. The concepts of User Interface (Human Factors) was not new, it was just a little newer in applying it to computers.
Jef Raskin had worked at Xerox, and he was tooting the "easier to use" trumpet, with his vision of what that meant. He brought some of those ideas from Xerox, but he had brought some of those ideas TO Xerox as well. Later, he convinced Jobs to visit Xerox PARC, and Jobs became an immediate convert (for ease of use).
What Jobs saw at Xerox was a prototype Smalltalk development system. He did not see either a working ALTO or Star (which was developed much later).
Apple paid
Jobs was so hot on the concepts of UI, and the living Demos he say, that he, later, negotiated a deal with Xerox. He gave Xerox a large sum of stock in Apple (worth Millions) if he could come back, and bring some programmers -- to inspire them more on the concepts of GUI. This was like a one-day tour. This was agreed to by Xerox, and so by no stretch of the imagination could this be called "ripping-off".
PARC was a research center -- meant to inspire development. But they did not really develop products (in the commercial sense), they developed ideas. Saying that Apple learning some of the base concepts and then applying them was "ripping-off" is like saying that Air-Bags are ripping off Newton -- because Air Bags work because they adhere to some of the laws of physics first expressed by Sir Isaac. A silly silly argument. Knowledge builds on knowledge. Xerox didn't see Apple as competition, that is why they let them in -- but they charged Apple, since Xerox believed that their research had value.
Apple was creating a product, and so they hired some of the same researchers from Xerox, to be brought to Apple to work on the Mac and Lisa projects. Those researches state quite clearly that the goals and implementation were quite different between Xerox and Apple. The following is an exchange between two of those researchers, and should give you an idea of how much the Mac contributed to the concepts of UI
