Casey: Windows stole everything from Mac, the whole invention of Windows was stolen from Apple
You're right about this in one way and wrong in another.
We're specifically talking about Mac OSX here, and OSX is not based on the original Apple operating system - everything up to OS9 was, but OSX is based on the software that Steve Jobs created at NeXT (the company he started after he was fired from Apple).
Since that point, Apple have taken many ideas from Microsoft, including:
The Finder Sidebar (first appeared in XP in 2001, showed up two years later on Mac OSX 10.3 Panther)
The Path Bar
Mac OS X 10.5 Leopard added an optional Path bar at the bottom of folder windows to display the path of any selected file or folder. Double-clicking a folder in the path opens that folder. Drag (or Option-drag) a file to move or copy it to one of the folders in the path. This feature first appeared as the Address bar in Windows Vista, which began appearing nearly a year before Leopard shipped. The Windows version has a bit more functionality, in that you can click an arrow next to a folder in a path to get to anything inside it.
Back and Forward buttons (like those in Web Browsers) in Folder systems - first appeared in Win2000, showed up later in OSX 10.2 Jaguar
Remote Desktop Connection - first showed up in XP, later showed up in OSX 10.5 Leopard. Microsoft even created a Mac version of RDC for free, before Apple wrote their own version.
Control Panel/System Preferences:
Before Mac OS X, Mac system settings were found in a set of separate files called control panels. Microsoft took the name, but put all the settings in one convenient place. For Mac OS X 10.0 Cheetah, Apple stole Microsoft's idea and called it System Preferences. Unlike the Windows Control Panel, the Mac's System Preferences doesn't open additional windows, and it tends to have a simpler user interface.
Alt-Tab shortcut to switch between running programs:
Since 1990's Windows 3, Alt-Tab has enabled users to easily switch between running applications. Apple added the feature using Command-Tab in Mac OS X 10.3 Panther in 2003. In recent versions, the command brings up a horizontal menu of icons. Apple, however, added functionality -- the ability to navigate the menu with the Command and arrow keys that Microsoft copied and added to Vista. Windows Vista also added previews of the windows themselves with the Flip 3D feature in the Aero theme.
Realistically both companies have ripped off each other in lots of different ways though, there's no denying that.
Xerox definitely got fucked though, but Jobs claim that Windows directly ripped off Apple's software is dubious, because there's no evidence to substantiate that Bill was aware of what Apple were doing (he was never hired by them from what I can see). Let's not forget that Apple lost their infringement lawsuit against Microsoft.
The GUI had its roots in the 1950s but was not developed until the 1970s when a group at the Xerox Palo Alto Research Center (PARC) developed the Alto, a GUI-based computer. The Alto was the size of a large desk, and Xerox believed it unmarketable. Jobs took a tour of PARC in 1979, and saw the future of personal computing in the Alto. Although much of the Interface of both the Lisa and the Mac was based (at least intellectually) heavily on the work done at PARC, and many of the engineers there later left to join Apple, much of the Mac OS was written before Job's visit to PARC. When Jobs accused Bill Gates of Microsoft of stealing the GUI from Apple and using it in Windows 1.0, Gates fired back:
No, Steve, I think its more like we both have a rich neighbor named Xerox, and you broke in to steal the TV set, and you found out I'd been there first, and you said. "Hey that's no fair! I wanted to steal the TV set!
The fact that both Apple and Microsoft had gotten the idea of the GUI from Xerox put a major dent in Apple's lawsuit against Microsoft over the GUI several years later. Although much of The Mac OS is original, it was similar enough to the old Alto GUI to make a "look and feel" suit against Microsoft dubious.