tell application "iTunes"
    set libPlaylist to library playlist "Library" of source "Library"
    set aTrack to item 1 of file tracks of libPlaylist
    set trackPath to (location of aTrack) --> alias "..."
    set posixPath to POSIX path of trackPath --> "/Volumes/<disk>/iTunes Library/Music/<artist>/<album>/<title.ext>"

set {oldTID, AppleScript's text item delimiters} to {AppleScript's text item delimiters, "/"}
set theList to text items of posixPath
set AppleScript's text item delimiters to oldTID
set iTunesMediaLoc to "/" & item 2 of theList & "/" & item 3 of theList & "/" & item 4 of theList & "/"

end tell