FileInfo.com - The File Extensions Resource

.PREFPANE File Extension

File Type	Mac OS X System Preference Pane
File Format	File
Common?	No
File Description	Adds a system preference to the Mac OS X System Preferences window; Apple preferences are stored in System->Library->PreferencePanes, while third-party preferences are stored in the Library->PreferencePanes directory
Program(s) that open prefpane files	Mac: Used by the Mac OS X operating system

Information from FileInfo.com - The File Extensions Resource.
http://www.fileinfo.com/extension/prefpane