As I am an ass, I didn't find a way to get which playlist is selected in the scroll area listing them.
Maybe GUIScripting was a way to get the wanted info but I decided to use an other way.
tell application "iTunes"
set theSelection to the selection
if theSelection is {} then
set thePlaylists to (name of every playlist)
# Choose the name of the playlist whose contents will be copied
tell me to set thePlaylist to choose from list thePlaylists
# Exit if you clicked the Cancel button (or pressed Escape)
if thePlaylist is false then error number -128
# Grab the list of aliases to files of tracks from the chosen playlist
set selectedSourceFiles to location of tracks of playlist item 1 of thePlaylist
else
# Grab the list of aliases to files of selected tracks
set selectedSourceFiles to location of theSelection
end if
end tell
# Copy every file in a defined folder on the desktop ( it creates it if it doesn’t exist)
do shell script "ditto " & quoted form of POSIX path of selectedSourceFiles & space & quoted form of POSIX path of ((path to desktop as text) & "my tunes:")