Yes, they built a mouse and shipped it as part of an integrated product, but it had been invented by others more than a decade earlier. It had even shipped in a product well before they did it. PARC is actually in pretty much the same position there that you're putting Apple - they took an existing idea and made it a bit more commercial than it had been. Englebart's mouse was unreliable and uncommerical; PARC's mouse was more practical to make, more reliable, but way too expensive; Apple's mouse was finally reliable and cheap.

http://en.wikipedia.org/wiki/Mouse_%28computing%29#Early_mic...