The philosophies behind window management for Microsoft and Apple OSs are very different. By understanding these differences, you can learn to use each one more effectively.
First things first… there is not a Maximize button is OS X. When you click the little green Zoom orb in the upper left hand corner of an OS X window, it is not the same as click the Maximize button in XP/Vista.
In XP/Vista, *that* button causes the window to cover the screen except for the taskbar. In OS X *that* button might do a bunch of different stuff because it is really controlled by the app. Typically, the green zoom button will resize the window just large enough to show all contents of the window.
If clicked a second time, both of these windows will “restore” the screen to the previously set user size (or the size previously set by manually resizing the screen). In XP/Vista the button actually changes to the Restore button to show this; in OS X the green Zoom button look is unchanging.
In some OS X applications, holding the option button while clicking the Zoom orb will cause it to act like a Maximize button. However, as it controlled by the application, this is not universal.