General/SystemPreferences is an Application built-in to Mac OS X which allows the user to alter system-wide preferences - i.e. preferences that will affect the whole OS and not just one application.
The application basically allows selection of different preferencePanes (commonly called prefpanes)
It is a Cocoa application and these panes are bundles that are loaded dynamically.
This means you can write your own prefpanes by subclassing General/NSPreferencePane
See also General/NSUserDefaults and General/CFPreferences.
General/NSUserDefaults seems to allow only storing data under the com.apple.systempreferences domain, not under your own domain. For that, you must use General/CFPreferences, either directly or by subclassing General/NSUserDefaults.
You may also use apple private methods of General/NSUserDefaults�:
@interface General/NSUserDefaults (General/ApplePrivate)