[mattyd]

subject says it all. would like to have iTunes automatically quit when switching between users (my roommate and i keep having to bother one another to log in and quit iTunes so the other can use it).

[gorickey]

Never used this before; however, sounds like EXACTLY what you are looking for...

iTunes interuser-Remote (iTiR) 2.0

[mjarski15]

If you both have admin permission, you can sudo kill ### (application Id number from top) in terminal. That usually what I do. Hope it helps

edit- also you can use the activity monitor app in the utilities folder to quit a process. Just change the tab on the right side to show other user processes, select iTunes, and press the quit a process button.