Apple's Magic Mouse is a unique input device that offers a multitouch surface for scrolling and performing various other functions in OS X. When it's connected to your Mac, the Mouse system preferences will change from a view that shows simple settings for speed and scrolling behaviors to options for the various finger gestures supported on the Magic Mouse. However, for some people the Magic Mouse settings will not appear and it will show the standard mouse options instead.
The Magic Mouse is ultimately a Bluetooth input device, so if the driver for the Magic Mouse does not load properly, then its basic pointing and clicking functions will be interpreted as they would be for any generic mouse. However, because the touch surface is not a standard mouse component, the basic mouse drivers in OS X will not recognize it and it will not function, even for basic scrolling features.
For some reason, Apple's Magic Mouse drivers will not load if some third-party mouse drivers are installed on the system, so if you turn on and pair your Magic Mouse with your Mac and the settings for the mouse do not appear, check to see if you have a third-party mouse driver installed (as for another pointing device, or even a generic USB input handler).
Some of these that people might have installed on their systems are driver packages from third-party mouse manufacturers (such as Logitech or Microsoft), USB Overdrive, BetterTouchTool, Jitouch, and drivers for other input-managing devices. Uninstall these options and restart the system, and the Magic Mouse settings should reappear.