File System with Actionscript3 on AIR

The File class includes static properties that let you reference commonly used directory locations. These static properties include:

File.applicationStorageDirectory	a storage directory unique to each installed AIR application
File.applicationDirectory	the read-only directory where the application is installed (along with any installed assets)
File.desktopDirectory	the user's desktop directory
File.documentsDirectory	the user's documents directory
File.userDirectory	the user directory

REFs:

http://help.adobe.com/en_US/FlashPlatform/reference/actionscript/3/flash/filesystem/File.html