The differences of Microsoft Windows and MacOS System:
♦ Windows ♦
It is the operating system by Microsoft, it is the one, that most home users use and it is also the one, that most games and stuff are developed for (maybe after game consoles like PlayStation etc.). Windows is a pre-compiled system, so you install a finished package on you computer and it is supposed to work right from the start. It can NOT be installed on any computer, not Power PCs for example.
♦ MacOS X ♦
This is a quite young system by the company apple, it is based on the first system: UNIX (very stable), but unlike UNIX it has a GUI (Graphical User Interface).
The current version is called OS X Tiger; it is also what I am using. OS X used to only work on special Apple Computers (the ones with the nice Design, iMac, iBook, etc.) but now they're making it compatible to the Intel-architecture too.