Hello, i've edit my button, with this code:
<plugin name="music" url="graphics/gk4/music.png" keep="true" align="bottom" x="200" y="$(MARGIN)" onover="set(blendmode,add);" onout="set(blendmode,screen);" />
everything is ok... (I'm very new and i want to understand the method of editing this kind of things... 
)
dut now i would like to know how to add music at the end of the first load of the pano and to turn off the music/turn on the music with this button... so ... help!! 