Running AppleScripts in iTunes
As of Snow Leopard (OS 10.6), Script Editor.app has been renamed AppleScript Editor.app and is located in your /Applications/Utilities/ folder. This article refers to Script Editor.app but AppleScript Editor.app also applies.
For single Users: naviagate to the [username]/Library/iTunes/ folder. If there is no folder named "Scripts" there, create one. Put your scripts in the "Scripts" folder and they will appear in iTunes' Scripts Menu.
• As of OS X 10.7 (Lion) the [username]/Library/iTunes/ folder is hidden by default. To make it temporarily visible, hold the Option key and select the Finder's "Go" menu. Select "Library" from the drop down menu that appears. (More ~/Library tips here.)
To make AppleScripts available to all Users, create a folder called "Scripts" and place it in the /Library/iTunes/ folder of your startup drive (you may have to create the "iTunes" folder as well as the "Scripts" folder; I think you can put the "iTunes Plug-Ins" folder here also, although it has nothing to do with AppleScript.).
You can organize your scripts to some degree by placing them in folders inside your Scripts folder. This will help you in the Finder; but the Scripts will still appear in one long list in iTunes' Scripts Menu. (Some other attachable applications let you use sub-folders which create a sub-menu heirarchy—hint hint, Apple!) I am not aware of any maximum limit on the number of scripts you can put in your Scripts folders. As of this writing, I have 288 that I use regularly or that I am working on
Users of Mac OS 10.3 and higher can assign keyboard shortcuts to AppleScripts in the iTunes Scripts Menu.
FastScripts from Red Sweater Software provides the ability to quickly and simply add and manage AppleScript keyboard shortcuts.
Another way of accessing scripts is with some sort of launcher. OS X has the Script Menu which let's you run scripts system-wide from a drop down menu in the Menu Bar. You add scripts to the Scripts Menu by putting them in the Library/Scripts/ folder for all users or the [username]/Library/Scripts/ folder for individual users. AppleScripting options regarding the global Script menu can be found, perhaps not so obviously, in AppleScript Editor's Preferences.
You can load AppleScript applets (applications) into the Finder's toolbar by drag and drop, or you can "keep" them in the Dock.
AppleScripting components are automatically installed by OS X, so unless you've gone and done something crazy, AppleScripting under OS X should be all set.